Opinions

Justice O’Connor announced the judgment of the Court and delivered an opinion, in which The Chief Justice, Justice Kennedy, and Justice Breyer join.
At this difficult time in our Nation’s history, we are called upon to consider the legality of the Government’s detention of a United States citizen on United States soil as an “enemy combatant” and to address the process that is constitutionally owed to one who seeks to challenge his classification as such. The United States Court of Appeals for the Fourth Circuit held that petitioner’s detention was legally authorized and that he was entitled to no further opportunity to challenge his enemy-combatant label. We now vacate and remand. We hold that although Congress authorized the detention of combatants in the narrow circumstances alleged here, due process demands that a citizen held in the United States as an enemy combatant be given a meaningful opportunity to contest the factual basis for that detention before a neutral decisionmaker.

I
On September 11, 2001, the al Qaeda terrorist network used hijacked commercial airliners to attack prominent targets in the United States. Approximately 3,000 people were killed in those attacks. One week later, in response to these “acts of treacherous violence,” Congress passed a resolution authorizing the President to “use all necessary and appropriate force against those nations, organizations, or persons he determines planned, authorized, committed, or aided the terrorist attacks” or “harbored such organizations or persons, in order to prevent any future acts of international terrorism against the United States by such nations, organizations or persons.” Authorization for Use of Military Force (“the AUMF”), 115 Stat. 224. Soon thereafter, the President ordered United States Armed Forces to Afghanistan, with a mission to subdue al Qaeda and quell the Taliban regime that was known to support it.

This case arises out of the detention of a man whom the Government alleges took up arms with the Taliban during this conflict. His name is Yaser Esam Hamdi. Born an American citizen in Louisiana in 1980, Hamdi moved with his family to Saudi Arabia as a child. By 2001, the parties agree, he resided in Afghanistan. At some point that year, he was seized by members of the Northern Alliance, a coalition of military groups opposed to the Taliban government, and eventually was turned over to the United States military. The Government asserts that it initially detained and interrogated Hamdi in Afghanistan before transferring him to the United States Naval Base in Guantanamo Bay in January 2002. In April 2002, upon learning that Hamdi is an American citizen, authorities transferred him to a naval brig in Norfolk, Virginia, where he remained until a recent transfer to a brig in Charleston, South Carolina. The Government contends that Hamdi is an “enemy combatant,” and that this status justifies holding him in the United States indefinitely—without formal charges or proceedings—unless and until it makes the determination that access to counsel or further process is warranted.

In June 2002, Hamdi’s father, Esam Fouad Hamdi, filed the present petition for a writ of habeas corpus under 28 U. S. C. §2241 in the Eastern District of Virginia, naming as petitioners his son and himself as next friend. The elder Hamdi alleges in the petition that he has had no contact with his son since the Government took custody of him in 2001, and that the Government has held his son “without access to legal counsel or notice of any charges pending against him.” App. 103, 104. The petition contends that Hamdi’s detention was not legally authorized. Id., at 105. It argues that, “[a]s an American citizen, … Hamdi enjoys the full protections of the Constitution,” and that Hamdi’s detention in the United States without charges, access to an impartial tribunal, or assistance of counsel “violated and continue[s] to violate the Fifth and Fourteenth Amendments to the United States Constitution.” Id., at 107. The habeas petition asks that the court, among other things, (1) appoint counsel for Hamdi; (2) order respondents to cease interrogating him; (3) declare that he is being held in violation of the Fifth and Fourteenth Amendments; (4) “[t]o the extent Respondents contest any material factual allegations in this Petition, schedule an evidentiary hearing, at which Petitioners may adduce proof in support of their allegations”; and (5) order that Hamdi be released from his “unlawful custody.” Id., at 108–109. Although his habeas petition provides no details with regard to the factual circumstances surrounding his son’s capture and detention, Hamdi’s father has asserted in documents found elsewhere in the record that his son went to Afghanistan to do “relief work,” and that he had been in that country less than two months before September 11, 2001, and could not have received military training. Id., at 188–189. The 20-year-old was traveling on his own for the first time, his father says, and “[b]ecause of his lack of experience, he was trapped in Afghanistan once that military campaign began.” Id., at 188–189.

The District Court found that Hamdi’s father was a proper next friend, appointed the federal public defender as counsel for the petitioners, and ordered that counsel be given access to Hamdi. Id., at 113–116. The United States Court of Appeals for the Fourth Circuit reversed that order, holding that the District Court had failed to extend appropriate deference to the Government’s security and intelligence interests. 296 F. 3d 278, 279, 283 (2002). It directed the District Court to consider “the most cautious procedures first,” id., at 284, and to conduct a deferential inquiry into Hamdi’s status, id., at 283. It opined that “if Hamdi is indeed an ‘enemy combatant’ who was captured during hostilities in Afghanistan, the government’s present detention of him is a lawful one.” Ibid.

On remand, the Government filed a response and a motion to dismiss the petition. It attached to its response a declaration from one Michael Mobbs (hereinafter “Mobbs Declaration”), who identified himself as Special Advisor to the Under Secretary of Defense for Policy. Mobbs indicated that in this position, he has been “substantially involved with matters related to the detention of enemy combatants in the current war against the al Qaeda terrorists and those who support and harbor them (including the Taliban).” App. 148. He expressed his “familiar[ity]” with Department of Defense and United States military policies and procedures applicable to the detention, control, and transfer of al Qaeda and Taliban personnel, and declared that “[b]ased upon my review of relevant records and reports, I am also familiar with the facts and circumstances related to the capture of … Hamdi and his detention by U. S. military forces.” Ibid.

Mobbs then set forth what remains the sole evidentiary support that the Government has provided to the courts for Hamdi’s detention. The declaration states that Hamdi “traveled to Afghanistan” in July or August 2001, and that he thereafter “affiliated with a Taliban military unit and received weapons training.” Ibid. It asserts that Hamdi “remained with his Taliban unit following the attacks of September 11” and that, during the time when Northern Alliance forces were “engaged in battle with the Taliban,” “Hamdi’s Taliban unit surrendered” to those forces, after which he “surrender[ed] his Kalishnikov assault rifle” to them. Id., at 148–149. The Mobbs Declaration also states that, because al Qaeda and the Taliban “were and are hostile forces engaged in armed conflict with the armed forces of the United States,” “individuals associated with” those groups “were and continue to be enemy combatants.” Id., at 149. Mobbs states that Hamdi was labeled an enemy combatant “[b]ased upon his interviews and in light of his association with the Taliban.” Ibid. According to the declaration, a series of “U. S. military screening team[s]” determined that Hamdi met “the criteria for enemy combatants,” and “a subsequent interview of Hamdi has confirmed that he surrendered and gave his firearm to Northern Alliance forces, which supports his classification as an enemy combatant.” Id., at 149–150.

After the Government submitted this declaration, the Fourth Circuit directed the District Court to proceed in accordance with its earlier ruling and, specifically, to “ ‘consider the sufficiency of the Mobbs Declaration as an independent matter before proceeding further.’ ” 316 F. 3d at 450, 462 (2003). The District Court found that the Mobbs Declaration fell “far short” of supporting Hamdi’s detention. App. 292. It criticized the generic and hearsay nature of the affidavit, calling it “little more than the government’s ‘say-so.’ ” Id., at 298. It ordered the Government to turn over numerous materials for in camera review, including copies of all of Hamdi’s statements and the notes taken from interviews with him that related to his reasons for going to Afghanistan and his activities therein; a list of all interrogators who had questioned Hamdi and their names and addresses; statements by members of the Northern Alliance regarding Hamdi’s surrender and capture; a list of the dates and locations of his capture and subsequent detentions; and the names and titles of the United States Government officials who made the determinations that Hamdi was an enemy combatant and that he should be moved to a naval brig. Id., at 185–186. The court indicated that all of these materials were necessary for “meaningful judicial review” of whether Hamdi’s detention was legally authorized and whether Hamdi had received sufficient process to satisfy the Due Process Clause of the Constitution and relevant treaties or military regulations. Id., at 291–292.

The Government sought to appeal the production order, and the District Court certified the question of whether the Mobbs Declaration, “ ‘standing alone, is sufficient as a matter of law to allow meaningful judicial review of [Hamdi’s] classification as an enemy combatant.’ ” 316 F. 3d, at 462. The Fourth Circuit reversed, but did not squarely answer the certified question. It instead stressed that, because it was “undisputed that Hamdi was captured in a zone of active combat in a foreign theater of conflict,” no factual inquiry or evidentiary hearing allowing Hamdi to be heard or to rebut the Government’s assertions was necessary or proper. Id., at 459. Concluding that the factual averments in the Mobbs Declaration, “if accurate,” provided a sufficient basis upon which to conclude that the President had constitutionally detained Hamdi pursuant to the President’s war powers, it ordered the habeas petition dismissed. Id., at 473. The Fourth Circuit emphasized that the “vital purposes” of the detention of uncharged enemy combatants—preventing those combatants from rejoining the enemy while relieving the military of the burden of litigating the circumstances of wartime captures halfway around the globe—were interests “directly derived from the war powers of Articles I and II.” Id., at 465–466. In that court’s view, because “Article III contains nothing analogous to the specific powers of war so carefully enumerated in Articles I and II,” id., at 463, separation of powers principles prohibited a federal court from “delv[ing] further into Hamdi’s status and capture,” id., at 473. Accordingly, the District Court’s more vigorous inquiry “went far beyond the acceptable scope of review.” Ibid.

On the more global question of whether legal authorization exists for the detention of citizen enemy combatants at all, the Fourth Circuit rejected Hamdi’s arguments that 18 U. S. C. §4001(a) and Article 5 of the Geneva Convention rendered any such detentions unlawful. The court expressed doubt as to Hamdi’s argument that §4001(a), which provides that “[n]o citizen shall be imprisoned or otherwise detained by the United States except pursuant to an Act of Congress,” required express congressional authorization of detentions of this sort. But it held that, in any event, such authorization was found in the post-September 11 Authorization for Use of Military Force. 316 F. 3d, at 467. Because “capturing and detaining enemy combatants is an inherent part of warfare,” the court held, “the ‘necessary and appropriate force’ referenced in the congressional resolution necessarily includes the capture and detention of any and all hostile forces arrayed against our troops.” Ibid. ; see also id., at 467–468 (noting that Congress, in 10 U. S. C. §956(5), had specifically authorized the expenditure of funds for keeping prisoners of war and persons whose status was determined “to be similar to prisoners of war,” and concluding that this appropriation measure also demonstrated that Congress had “authorized [these individuals’] detention in the first instance”). The court likewise rejected Hamdi’s Geneva Convention claim, concluding that the convention is not self-executing and that, even if it were, it would not preclude the Executive from detaining Hamdi until the cessation of hostilities. 316 F. 3d, at 468–469.

Finally, the Fourth Circuit rejected Hamdi’s contention that its legal analyses with regard to the authorization for the detention scheme and the process to which he was constitutionally entitled should be altered by the fact that he is an American citizen detained on American soil. Relying on Ex parte Quirin, 317 U. S. 1 (1942), the court emphasized that “[o]ne who takes up arms against the United States in a foreign theater of war, regardless of his citizenship, may properly be designated an enemy combatant and treated as such.” 316 F.3d, at 475. “The privilege of citizenship,” the court held, “entitles Hamdi to a limited judicial inquiry into his detention, but only to determine its legality under the war powers of the political branches. At least where it is undisputed that he was present in a zone of active combat operations, we are satisfied that the Constitution does not entitle him to a searching review of the factual determinations underlying his seizure there.” Ibid.

The Fourth Circuit denied rehearing en banc, 337 F. 3d 335 (2003), and we granted certiorari. 540 U. S. __ (2004). We now vacate the judgment below and remand.

II
The threshold question before us is whether the Executive has the authority to detain citizens who qualify as “enemy combatants.” There is some debate as to the proper scope of this term, and the Government has never provided any court with the full criteria that it uses in classifying individuals as such. It has made clear, however, that, for purposes of this case, the “enemy combatant” that it is seeking to detain is an individual who, it alleges, was “ ‘part of or supporting forces hostile to the United States or coalition partners’ ” in Afghanistan and who “ ‘engaged in an armed conflict against the United States’ ” there. Brief for Respondents 3. We therefore answer only the narrow question before us: whether the detention of citizens falling within that definition is authorized.

The Government maintains that no explicit congressional authorization is required, because the Executive possesses plenary authority to detain pursuant to Article II of the Constitution. We do not reach the question whether Article II provides such authority, however, because we agree with the Government’s alternative position, that Congress has in fact authorized Hamdi’s detention, through the AUMF.

Our analysis on that point, set forth below, substantially overlaps with our analysis of Hamdi’s principal argument for the illegality of his detention. He posits that his detention is forbidden by 18 U. S. C. §4001(a). Section 4001(a) states that “[n]o citizen shall be imprisoned or otherwise detained by the United States except pursuant to an Act of Congress.” Congress passed §4001(a) in 1971 as part of a bill to repeal the Emergency Detention Act of 1950, 50 U. S. C. §811 et seq., which provided procedures for executive detention, during times of emergency, of individuals deemed likely to engage in espionage or sabotage. Congress was particularly concerned about the possibility that the Act could be used to reprise the Japanese internment camps of World War II. H. R. Rep. No. 92–116 (1971); id., at 4 (“The concentration camp implications of the legislation render it abhorrent”). The Government again presses two alternative positions. First, it argues that §4001(a), in light of its legislative history and its location in Title 18, applies only to “the control of civilian prisons and related detentions,” not to military detentions. Brief for Respondents 21. Second, it maintains that §4001(a) is satisfied, because Hamdi is being detained “pursuant to an Act of Congress”—the AUMF. Id., at 21–22. Again, because we conclude that the Government’s second assertion is correct, we do not address the first. In other words, for the reasons that follow, we conclude that the AUMF is explicit congressional authorization for the detention of individuals in the narrow category we describe (assuming, without deciding, that such authorization is required), and that the AUMF satisfied §4001(a)’s requirement that a detention be “pursuant to an Act of Congress” (assuming, without deciding, that §4001(a) applies to military detentions).

The AUMF authorizes the President to use “all necessary and appropriate force” against “nations, organizations, or persons” associated with the September 11, 2001, terrorist attacks. 115 Stat. 224. There can be no doubt that individuals who fought against the United States in Afghanistan as part of the Taliban, an organization known to have supported the al Qaeda terrorist network responsible for those attacks, are individuals Congress sought to target in passing the AUMF. We conclude that detention of individuals falling into the limited category we are considering, for the duration of the particular conflict in which they were captured, is so fundamental and accepted an incident to war as to be an exercise of the “necessary and appropriate force” Congress has authorized the President to use.

The capture and detention of lawful combatants and the capture, detention, and trial of unlawful combatants, by “universal agreement and practice,” are “important incident[s] of war.” Ex parte Quirin, 317 U. S., at 28. The purpose of detention is to prevent captured individuals from returning to the field of battle and taking up arms once again. Naqvi, Doubtful Prisoner-of-War Status, 84 Int’l Rev. Red Cross 571, 572 (2002) (“[C]aptivity in war is ‘neither revenge, nor punishment, but solely protective custody, the only purpose of which is to prevent the prisoners of war from further participation in the war’ ” (quoting decision of Nuremberg Military Tribunal, reprinted in 41 Am. J. Int’l L. 172, 229 (1947)); W. Winthrop, Military Law and Precedents 788 (rev. 2d ed. 1920) (“The time has long passed when ‘no quarter’ was the rule on the battlefield …. It is now recognized that ‘Captivity is neither a punishment nor an act of vengeance,’ but ‘merely a temporary detention which is devoid of all penal character.’ … ‘A prisoner of war is no convict; his imprisonment is a simple war measure.’ ” (citations omitted); cf. In re Territo, 156 F. 2d 142, 145 (CA9 1946) (“The object of capture is to prevent the captured individual from serving the enemy. He is disarmed and from then on must be removed as completely as practicable from the front, treated humanely, and in time exchanged, repatriated, or otherwise released” (footnotes omitted)).

There is no bar to this Nation’s holding one of its own citizens as an enemy combatant. In Quirin, one of the detainees, Haupt, alleged that he was a naturalized United States citizen. 317 U. S., at 20. We held that “[c]itizens who associate themselves with the military arm of the enemy government, and with its aid, guidance and direction enter this country bent on hostile acts, are enemy belligerents within the meaning of … the law of war.” Id. , at 37–38. While Haupt was tried for violations of the law of war, nothing in Quirin suggests that his citizenship would have precluded his mere detention for the duration of the relevant hostilities. See id. , at 30–31. See also Lieber Code, ¶ ;153, Instructions for the Government of Armies of the United States in the Field, Gen. Order No. 100 (1863), reprinted in 2 Lieber, Miscellaneous Writings, p. 273 (contemplating, in code binding the Union Army during the Civil War, that “captured rebels” would be treated “as prisoners of war”). Nor can we see any reason for drawing such a line here. A citizen, no less than an alien, can be “part of or supporting forces hostile to the United States or coalition partners” and “engaged in an armed conflict against the United States,” Brief for Respondents 3; such a citizen, if released, would pose the same threat of returning to the front during the ongoing conflict.

In light of these principles, it is of no moment that the AUMF does not use specific language of detention. Because detention to prevent a combatant’s return to the battlefield is a fundamental incident of waging war, in permitting the use of “necessary and appropriate force,” Congress has clearly and unmistakably authorized detention in the narrow circumstances considered here.

Hamdi objects, nevertheless, that Congress has not authorized the indefinite detention to which he is now subject. The Government responds that “the detention of enemy combatants during World War II was just as ‘indefinite’ while that war was being fought.” Id., at 16. We take Hamdi’s objection to be not to the lack of certainty regarding the date on which the conflict will end, but to the substantial prospect of perpetual detention. We recognize that the national security underpinnings of the “war on terror,” although crucially important, are broad and malleable. As the Government concedes, “given its unconventional nature, the current conflict is unlikely to end with a formal cease-fire agreement.” Ibid. The prospect Hamdi raises is therefore not far-fetched. If the Government does not consider this unconventional war won for two generations, and if it maintains during that time that Hamdi might, if released, rejoin forces fighting against the United States, then the position it has taken throughout the litigation of this case suggests that Hamdi’s detention could last for the rest of his life.

It is a clearly established principle of the law of war that detention may last no longer than active hostilities. See Article 118 of the Geneva Convention (III) Relative to the Treatment of Prisoners of War, Aug. 12, 1949, [1955] 6 U. S. T. 3316, 3406, T. I. A. S. No. 3364 (“Prisoners of war shall be released and repatriated without delay after the cessation of active hostilities”). See also Article 20 of the Hague Convention (II) on Laws and Customs of War on Land, July 29, 1899, 32 Stat. 1817 (as soon as possible after “conclusion of peace”); Hague Convention (IV), supra, Oct. 18, 1907, 36 Stat. 2301(“conclusion of peace” (Art. 20)); Geneva Convention, supra, July 27, 1929, 47 Stat. 2055 (repatriation should be accomplished with the least possible delay after conclusion of peace (Art. 75)); Praust, Judicial Power to Determine the Status and Rights of Persons Detained without Trial, 44 Harv. Int’l L. J. 503, 510–511 (2003) (prisoners of war “can be detained during an armed conflict, but the detaining country must release and repatriate them ‘without delay after the cessation of active hostilities,’ unless they are being lawfully prosecuted or have been lawfully convicted of crimes and are serving sentences” (citing Arts. 118, 85, 99, 119, 129, Geneva Convention (III), 6 T. I.A. S., at 3384, 3392, 3406, 3418)).

Hamdi contends that the AUMF does not authorize indefinite or perpetual detention. Certainly, we agree that indefinite detention for the purpose of interrogation is not authorized. Further, we understand Congress’ grant of authority for the use of “necessary and appropriate force” to include the authority to detain for the duration of the relevant conflict, and our understanding is based on longstanding law-of-war principles. If the practical circumstances of a given conflict are entirely unlike those of the conflicts that informed the development of the law of war, that understanding may unravel. But that is not the situation we face as of this date. Active combat operations against Taliban fighters apparently are ongoing in Afghanistan. See, e.g., Constable, U. S. Launches New Operation in Afghanistan, Washington Post, Mar. 14, 2004, p. A22 (reporting that 13,500 United States troops remain in Afghanistan, including several thousand new arrivals); J. Abizaid, Dept. of Defense, Gen. Abizaid Central Command Operations Update Briefing, Apr. 30, 2004, http://www.defenselink.mil/transcripts/2004/tr20040430-1402.html (as visited June 8, 2004, and available in the Clerk of Court’s case file) (media briefing describing ongoing operations in Afghanistan involving 20,000 United States troops). The United States may detain, for the duration of these hostilities, individuals legitimately determined to be Taliban combatants who “engaged in an armed conflict against the United States.” If the record establishes that United States troops are still involved in active combat in Afghanistan, those detentions are part of the exercise of “necessary and appropriate force,” and therefore are authorized by the AUMF.

Ex parte Milligan, 4 Wall. 2, 125 (1866), does not undermine our holding about the Government’s authority to seize enemy combatants, as we define that term today. In that case, the Court made repeated reference to the fact that its inquiry into whether the military tribunal had jurisdiction to try and punish Milligan turned in large part on the fact that Milligan was not a prisoner of war, but a resident of Indiana arrested while at home there. Id., at 118, 131. That fact was central to its conclusion. Had Milligan been captured while he was assisting Confederate soldiers by carrying a rifle against Union troops on a Confederate battlefield, the holding of the Court might well have been different. The Court’s repeated explanations that Milligan was not a prisoner of war suggest that had these different circumstances been present he could have been detained under military authority for the duration of the conflict, whether or not he was a citizen.[ Footnote 1 ]

Moreover, as Justice Scalia acknowledges, the Court in Ex parte Quirin, 317 U. S. 1 (1942), dismissed the language of Milligan that the petitioners had suggested prevented them from being subject to military process. Post, at 17–18 (dissenting opinion). Clear in this rejection was a disavowal of the New York State cases cited in Milligan, 4 Wall., at 128–129, on which Justice Scalia relies. See id., at 128–129. Both Smith v. Shaw, 12 Johns. *257 (N. Y. 1815), and M’Connell v. Hampton, 12 Johns. *234 (N. Y. 1815), were civil suits for false imprisonment. Even accepting that these cases once could have been viewed as standing for the sweeping proposition for which Justice Scalia cites them—that the military does not have authority to try an American citizen accused of spying against his country during wartime— Quirin makes undeniably clear that this is not the law today. Haupt, like the citizens in Smith and M’Connell, was accused of being a spy. The Court in Quirin found him “subject to trial and punishment by [a] military tribunal[ ]” for those acts, and held that his citizenship did not change this result. 317 U. S., at 31, 37–38.

Quirin was a unanimous opinion. It both postdates and clarifies Milligan, providing us with the most apposite precedent that we have on the question of whether citizens may be detained in such circumstances. Brushing aside such precedent—particularly when doing so gives rise to a host of new questions never dealt with by this Court—is unjustified and unwise.

To the extent that Justice Scalia accepts the precedential value of Quirin, he argues that it cannot guide our inquiry here because “[i]n Quirin it was uncontested that the petitioners were members of enemy forces,” while Hamdi challenges his classification as an enemy combatant. Post, at 19. But it is unclear why, in the paradigm outlined by Justice Scalia, such a concession should have any relevance. Justice Scalia envisions a system in which the only options are congressional suspension of the writ of habeas corpus or prosecution for treason or some other crime. Post, at 1. He does not explain how his historical analysis supports the addition of a third option—detention under some other process after concession of enemy-combatant status—or why a concession should carry any different effect than proof of enemy-combatant status in a proceeding that comports with due process. To be clear, our opinion only finds legislative authority to detain under the AUMF once it is sufficiently clear that the individual is, in fact, an enemy combatant; whether that is established by concession or by some other process that verifies this fact with sufficient certainty seems beside the point.

Further, Justice Scalia largely ignores the context of this case: a United States citizen captured in a foreign combat zone. Justice Scalia refers to only one case involving this factual scenario—a case in which a United States citizen-POW (a member of the Italian army) from World War II was seized on the battlefield in Sicily and then held in the United States. The court in that case held that the military detention of that United States citizen was lawful. See In re Territo, 156 F. 2d, at 148.

Justice Scalia’s treatment of that case—in a footnote—suffers from the same defect as does his treatment of Quirin: Because Justice Scalia finds the fact of battlefield capture irrelevant, his distinction based on the fact that the petitioner “conceded” enemy combatant status is beside the point. See supra, at 15–16. Justice Scalia can point to no case or other authority for the proposition that those captured on a foreign battlefield (whether detained there or in U. S. territory) cannot be detained outside the criminal process.

Moreover, Justice Scalia presumably would come to a different result if Hamdi had been kept in Afghanistan or even Guantanamo Bay. See post, at 25 (Scalia, J., dissenting). This creates a perverse incentive. Military authorities faced with the stark choice of submitting to the full-blown criminal process or releasing a suspected enemy combatant captured on the battlefield will simply keep citizen-detainees abroad. Indeed, the Government transferred Hamdi from Guantanamo Bay to the United States naval brig only after it learned that he might be an American citizen. It is not at all clear why that should make a determinative constitutional difference.

III
Even in cases in which the detention of enemy combatants is legally authorized, there remains the question of what process is constitutionally due to a citizen who disputes his enemy-combatant status. Hamdi argues that he is owed a meaningful and timely hearing and that “extra-judicial detention [that] begins and ends with the submission of an affidavit based on third-hand hearsay” does not comport with the Fifth and Fourteenth Amendments. Brief for Petitioners 16. The Government counters that any more process than was provided below would be both unworkable and “constitutionally intolerable.” Brief for Respondents 46. Our resolution of this dispute requires a careful examination both of the writ of habeas corpus, which Hamdi now seeks to employ as a mechanism of judicial review, and of the Due Process Clause, which informs the procedural contours of that mechanism in this instance.

A
Though they reach radically different conclusions on the process that ought to attend the present proceeding, the parties begin on common ground. All agree that, absent suspension, the writ of habeas corpus remains available to every individual detained within the United States. U. S. Const., Art. I, §9, cl. 2 (“The Privilege of the Writ of Habeas Corpus shall not be suspended, unless when in Cases of Rebellion or Invasion the public Safety may require it”). Only in the rarest of circumstances has Congress seen fit to suspend the writ. See, e.g., Act of Mar. 3, 1863, ch. 81, §1, 12 Stat. 755; Act of April 20, 1871, ch. 22, §4, 17 Stat. 14. At all other times, it has remained a critical check on the Executive, ensuring that it does not detain individuals except in accordance with law. See INS v. St. Cyr, 533 U. S. 289, 301 (2001). All agree suspension of the writ has not occurred here. Thus, it is undisputed that Hamdi was properly before an Article III court to challenge his detention under 28 U. S. C. §2241. Brief for Respondents 12. Further, all agree that §2241 and its companion provisions provide at least a skeletal outline of the procedures to be afforded a petitioner in federal habeas review. Most notably, §2243 provides that “the person detained may, under oath, deny any of the facts set forth in the return or allege any other material facts,” and §2246 allows the taking of evidence in habeas proceedings by deposition, affidavit, or interrogatories.

The simple outline of §2241 makes clear both that Congress envisioned that habeas petitioners would have some opportunity to present and rebut facts and that courts in cases like this retain some ability to vary the ways in which they do so as mandated by due process. The Government recognizes the basic procedural protections required by the habeas statute, Id., at 37–38, but asks us to hold that, given both the flexibility of the habeas mechanism and the circumstances presented in this case, the presentation of the Mobbs Declaration to the habeas court completed the required factual development. It suggests two separate reasons for its position that no further process is due.

B
First, the Government urges the adoption of the Fourth Circuit’s holding below—that because it is “undisputed” that Hamdi’s seizure took place in a combat zone, the habeas determination can be made purely as a matter of law, with no further hearing or factfinding necessary. This argument is easily rejected. As the dissenters from the denial of rehearing en banc noted, the circumstances surrounding Hamdi’s seizure cannot in any way be characterized as “undisputed,” as “those circumstances are neither conceded in fact, nor susceptible to concession in law, because Hamdi has not been permitted to speak for himself or even through counsel as to those circumstances.” 337 F. 3d 335, 357 (CA4 2003) (Luttig, J., dissenting from denial of rehearing en banc); see also id., at 371–372 (Motz, J., dissenting from denial of rehearing en banc). Further, the “facts” that constitute the alleged concession are insufficient to support Hamdi’s detention. Under the definition of enemy combatant that we accept today as falling within the scope of Congress’ authorization, Hamdi would need to be “part of or supporting forces hostile to the United States or coalition partners” and “engaged in an armed conflict against the United States” to justify his detention in the United States for the duration of the relevant conflict. Brief for Respondents 3. The habeas petition states only that “[w]hen seized by the United States Government, Mr. Hamdi resided in Afghanistan.” App. 104. An assertion that one resided in a country in which combat operations are taking place is not a concession that one was “ captured in a zone of active combat operations in a foreign theater of war,” 316 F. 3d, at 459 (emphasis added), and certainly is not a concession that one was “part of or supporting forces hostile to the United States or coalition partners” and “engaged in an armed conflict against the United States.” Accordingly, we reject any argument that Hamdi has made concessions that eliminate any right to further process.

C
The Government’s second argument requires closer consideration. This is the argument that further factual exploration is unwarranted and inappropriate in light of the extraordinary constitutional interests at stake. Under the Government’s most extreme rendition of this argument, “[r]espect for separation of powers and the limited institutional capabilities of courts in matters of military decision-making in connection with an ongoing conflict” ought to eliminate entirely any individual process, restricting the courts to investigating only whether legal authorization exists for the broader detention scheme. Brief for Respondents 26. At most, the Government argues, courts should review its determination that a citizen is an enemy combatant under a very deferential “some evidence” standard. Id., at 34 (“Under the some evidence standard, the focus is exclusively on the factual basis supplied by the Executive to support its own determination” (citing Superintendent, Mass. Correctional Institution at Walpole v. Hill, 472 U. S. 445, 455–457 (1985) (explaining that the some evidence standard “does not require” a “weighing of the evidence,” but rather calls for assessing “whether there is any evidence in the record that could support the conclusion”)). Under this review, a court would assume the accuracy of the Government’s articulated basis for Hamdi’s detention, as set forth in the Mobbs Declaration, and assess only whether that articulated basis was a legitimate one. Brief for Respondents 36; see also 316 F. 3d, at 473–474 (declining to address whether the “some evidence” standard should govern the adjudication of such claims, but noting that “[t]he factual averments in the [Mobbs] affidavit, if accurate, are sufficient to confirm” the legality of Hamdi’s detention).

In response, Hamdi emphasizes that this Court consistently has recognized that an individual challenging his detention may not be held at the will of the Executive without recourse to some proceeding before a neutral tribunal to determine whether the Executive’s asserted justifications for that detention have basis in fact and warrant in law. See, e.g., Zadvydas v. Davis, 533 U. S. 678, 690 (2001); Addington v. Texas, 441 U. S. 418, 425–427 (1979). He argues that the Fourth Circuit inappropriately “ceded power to the Executive during wartime to define the conduct for which a citizen may be detained, judge whether that citizen has engaged in the proscribed conduct, and imprison that citizen indefinitely,” Brief for Petitioners 21, and that due process demands that he receive a hearing in which he may challenge the Mobbs Declaration and adduce his own counter evidence. The District Court, agreeing with Hamdi, apparently believed that the appropriate process would approach the process that accompanies a criminal trial. It therefore disapproved of the hearsay nature of the Mobbs Declaration and anticipated quite extensive discovery of various military affairs. Anything less, it concluded, would not be “meaningful judicial review.” App. 291.

Both of these positions highlight legitimate concerns. And both emphasize the tension that often exists between the autonomy that the Government asserts is necessary in order to pursue effectively a particular goal and the process that a citizen contends he is due before he is deprived of a constitutional right. The ordinary mechanism that we use for balancing such serious competing interests, and for determining the procedures that are necessary to ensure that a citizen is not “deprived of life, liberty, or property, without due process of law,” U. S. Const., Amdt. 5, is the test that we articulated in Mathews v. Eldridge, 424 U. S. 319 (1976). See, e.g., Heller v. Doe, 509 U. S. 312, 330–331 (1993); Zinermon v. Burch, 494 U. S. 113, 127–128 (1990); United States v. Salerno, 481 U. S. 739, 746 (1987); Schall v. Martin, 467 U. S. 253, 274–275 (1984); Addington v. Texas, supra, at 425. Mathews dictates that the process due in any given instance is determined by weighing “the private interest that will be affected by the official action” against the Government’s asserted interest, “including the function involved” and the burdens the Government would face in providing greater process. 424 U. S., at 335. The Mathews calculus then contemplates a judicious balancing of these concerns, through an analysis of “the risk of an erroneous deprivation” of the private interest if the process were reduced and the “probable value, if any, of additional or substitute safeguards.” Ibid. We take each of these steps in turn.

1
It is beyond question that substantial interests lie on both sides of the scale in this case. Hamdi’s “private interest … affected by the official action,” ibid., is the most elemental of liberty interests—the interest in being free from physical detention by one’s own government. Foucha v. Louisiana, 504 U. S. 71, 80 (1992) (“Freedom from bodily restraint has always been at the core of the liberty protected by the Due Process Clause from arbitrary governmental action”); see also Parham v. J. R., 442 U. S. 584, 600 (1979) (noting the “substantial liberty interest in not being confined unnecessarily”). “In our society liberty is the norm,” and detention without trial “is the carefully limited exception.” Salerno, supra, at 755. “We have always been careful not to ‘minimize the importance and fundamental nature’ of the individual’s right to liberty,” Foucha, supra, at 80 (quoting Salerno, supra, at 750), and we will not do so today.

Nor is the weight on this side of the Mathews scale offset by the circumstances of war or the accusation of treasonous behavior, for “[i]t is clear that commitment for any purpose constitutes a significant deprivation of liberty that requires due process protection,” Jones v. United States, 463 U. S. 354, 361 (1983) (emphasis added; internal quotation marks omitted), and at this stage in the Mathews calculus, we consider the interest of the erroneously detained individual. Carey v. Piphus, 435 U. S. 247, 259 (1978) (“Procedural due process rules are meant to protect persons not from the deprivation, but from the mistaken or unjustified deprivation of life, liberty, or property”); see also id., at 266 (noting “the importance to organized society that procedural due process be observed,” and emphasizing that “the right to procedural due process is ‘absolute’ in the sense that it does not depend upon the merits of a claimant’s substantive assertions”). Indeed, as amicus briefs from media and relief organizations emphasize, the risk of erroneous deprivation of a citizen’s liberty in the absence of sufficient process here is very real. See Brief for AmeriCares et al. as Amici Curiae 13–22 (noting ways in which “[t]he nature of humanitarian relief work and journalism present a significant risk of mistaken military detentions”). Moreover, as critical as the Government’s interest may be in detaining those who actually pose an immediate threat to the national security of the United States during ongoing international conflict, history and common sense teach us that an unchecked system of detention carries the potential to become a means for oppression and abuse of others who do not present that sort of threat. See Ex parte Milligan, 4 Wall., at 125 (“[The Founders] knew—the history of the world told them—the nation they were founding, be its existence short or long, would be involved in war; how often or how long continued, human foresight could not tell; and that unlimited power, wherever lodged at such a time, was especially hazardous to freemen”). Because we live in a society in which “[m]ere public intolerance or animosity cannot constitutionally justify the deprivation of a person’s physical liberty,” O’Connor v. Donaldson, 422 U. S. 563, 575 (1975), our starting point for the Mathews v. Eldridge analysis is unaltered by the allegations surrounding the particular detainee or the organizations with which he is alleged to have associated. We reaffirm today the fundamental nature of a citizen’s right to be free from involuntary confinement by his own government without due process of law, and we weigh the opposing governmental interests against the curtailment of liberty that such confinement entails.

2
On the other side of the scale are the weighty and sensitive governmental interests in ensuring that those who have in fact fought with the enemy during a war do not return to battle against the United States. As discussed above, supra, at 10, the law of war and the realities of combat may render such detentions both necessary and appropriate, and our due process analysis need not blink at those realities. Without doubt, our Constitution recognizes that core strategic matters of warmaking belong in the hands of those who are best positioned and most politically accountable for making them. Department of Navy v. Egan, 484 U. S. 518, 530 (1988) (noting the reluctance of the courts “to intrude upon the authority of the Executive in military and national security affairs”); Youngstown Sheet & Tube Co. v. Sawyer, 343 U. S. 579, 587 (1952) (acknowledging “broad powers in military commanders engaged in day-to-day fighting in a theater of war”).

The Government also argues at some length that its interests in reducing the process available to alleged enemy combatants are heightened by the practical difficulties that would accompany a system of trial-like process. In its view, military officers who are engaged in the serious work of waging battle would be unnecessarily and dangerously distracted by litigation half a world away, and discovery into military operations would both intrude on the sensitive secrets of national defense and result in a futile search for evidence buried under the rubble of war. Brief for Respondents 46–49. To the extent that these burdens are triggered by heightened procedures, they are properly taken into account in our due process analysis.

3
Striking the proper constitutional balance here is of great importance to the Nation during this period of ongoing combat. But it is equally vital that our calculus not give short shrift to the values that this country holds dear or to the privilege that is American citizenship. It is during our most challenging and uncertain moments that our Nation’s commitment to due process is most severely tested; and it is in those times that we must preserve our commitment at home to the principles for which we fight abroad. See Kennedy v. Mendoza&nbhyph;Martinez, 372 U. S. 144, 164–165 (1963) (“The imperative necessity for safeguarding these rights to procedural due process under the gravest of emergencies has existed throughout our constitutional history, for it is then, under the pressing exigencies of crisis, that there is the greatest temptation to dispense with guarantees which, it is feared, will inhibit government action”); see also United States v. Robel, 389 U. S. 258, 264 (1967) (“It would indeed be ironic if, in the name of national defense, we would sanction the subversion of one of those liberties … which makes the defense of the Nation worthwhile”).

With due recognition of these competing concerns, we believe that neither the process proposed by the Government nor the process apparently envisioned by the District Court below strikes the proper constitutional balance when a United States citizen is detained in the United States as an enemy combatant. That is, “the risk of erroneous deprivation” of a detainee’s liberty interest is unacceptably high under the Government’s proposed rule, while some of the “additional or substitute procedural safeguards” suggested by the District Court are unwarranted in light of their limited “probable value” and the burdens they may impose on the military in such cases. Mathews, 424 U. S., at 335.

We therefore hold that a citizen-detainee seeking to challenge his classification as an enemy combatant must receive notice of the factual basis for his classification, and a fair opportunity to rebut the Government’s factual assertions before a neutral decisionmaker. See Cleveland Bd. of Ed. v. Loudermill, 470 U. S. 532, 542 (1985) (“An essential principle of due process is that a deprivation of life, liberty, or property ‘be preceded by notice and opportunity for hearing appropriate to the nature of the case’ ” (quoting Mullane v. Central Hanover Bank & Trust Co., 339 U. S. 306, 313 (1950)); Concrete Pipe & Products of Cal., Inc. v. Construction Laborers Pension Trust for Southern Cal., 508 U. S. 602, 617 (1993) (“due process requires a ‘neutral and detached judge in the first instance’ ” (quoting Ward v. Monroeville, 409 U. S. 57, 61–62 (1972)). “For more than a century the central meaning of procedural due process has been clear: ‘Parties whose rights are to be affected are entitled to be heard; and in order that they may enjoy that right they must first be notified.’ It is equally fundamental that the right to notice and an opportunity to be heard ‘must be granted at a meaningful time and in a meaningful manner.’ ” Fuentes v. Shevin, 407 U. S. 67, 80 (1972) (quoting Baldwin v. Hale, 1 Wall. 223, 233 (1864); Armstrong v. Manzo, 380 U. S. 545, 552 (1965) (other citations omitted)). These essential constitutional promises may not be eroded.

At the same time, the exigencies of the circumstances may demand that, aside from these core elements, enemy combatant proceedings may be tailored to alleviate their uncommon potential to burden the Executive at a time of ongoing military conflict. Hearsay, for example, may need to be accepted as the most reliable available evidence from the Government in such a proceeding. Likewise, the Constitution would not be offended by a presumption in favor of the Government’s evidence, so long as that presumption remained a rebuttable one and fair opportunity for rebuttal were provided. Thus, once the Government puts forth credible evidence that the habeas petitioner meets the enemy-combatant criteria, the onus could shift to the petitioner to rebut that evidence with more persuasive evidence that he falls outside the criteria. A burden-shifting scheme of this sort would meet the goal of ensuring that the errant tourist, embedded journalist, or local aid worker has a chance to prove military error while giving due regard to the Executive once it has put forth meaningful support for its conclusion that the detainee is in fact an enemy combatant. In the words of Mathews, process of this sort would sufficiently address the “risk of erroneous deprivation” of a detainee’s liberty interest while eliminating certain procedures that have questionable additional value in light of the burden on the Government. 424 U. S., at 335.[ Footnote 2 ]

We think it unlikely that this basic process will have the dire impact on the central functions of warmaking that the Government forecasts. The parties agree that initial captures on the battlefield need not receive the process we have discussed here; that process is due only when the determination is made to continue to hold those who have been seized. The Government has made clear in its briefing that documentation regarding battlefield detainees already is kept in the ordinary course of military affairs. Brief for Respondents 3–4. Any factfinding imposition created by requiring a knowledgeable affiant to summarize these records to an independent tribunal is a minimal one. Likewise, arguments that military officers ought not have to wage war under the threat of litigation lose much of their steam when factual disputes at enemy-combatant hearings are limited to the alleged combatant’s acts. This focus meddles little, if at all, in the strategy or conduct of war, inquiring only into the appropriateness of continuing to detain an individual claimed to have taken up arms against the United States. While we accord the greatest respect and consideration to the judgments of military authorities in matters relating to the actual prosecution of a war, and recognize that the scope of that discretion necessarily is wide, it does not infringe on the core role of the military for the courts to exercise their own time-honored and constitutionally mandated roles of reviewing and resolving claims like those presented here. Cf. Korematsu v. United States, 323 U. S. 214, 233–234 (1944) (Murphy, J., dissenting) (“[L]ike other claims conflicting with the asserted constitutional rights of the individual, the military claim must subject itself to the judicial process of having its reasonableness determined and its conflicts with other interests reconciled”); Sterling v. Constantin, 287 U. S. 378, 401 (1932) (“What are the allowable limits of military discretion, and whether or not they have been overstepped in a particular case, are judicial questions”).

In sum, while the full protections that accompany challenges to detentions in other settings may prove unworkable and inappropriate in the enemy-combatant setting, the threats to military operations posed by a basic system of independent review are not so weighty as to trump a citizen’s core rights to challenge meaningfully the Government’s case and to be heard by an impartial adjudicator.

D
In so holding, we necessarily reject the Government’s assertion that separation of powers principles mandate a heavily circumscribed role for the courts in such circumstances. Indeed, the position that the courts must forgo any examination of the individual case and focus exclusively on the legality of the broader detention scheme cannot be mandated by any reasonable view of separation of powers, as this approach serves only to condense power into a single branch of government. We have long since made clear that a state of war is not a blank check for the President when it comes to the rights of the Nation’s citizens. Youngstown Sheet & Tube, 343 U. S., at 587. Whatever power the United States Constitution envisions for the Executive in its exchanges with other nations or with enemy organizations in times of conflict, it most assuredly envisions a role for all three branches when individual liberties are at stake. Mistretta v. United States, 488 U. S. 361, 380 (1989) (it was “the central judgment of the Framers of the Constitution that, within our political scheme, the separation of governmental powers into three coordinate Branches is essential to the preservation of liberty”); Home Building & Loan Assn. v. Blaisdell, 290 U. S. 398, 426 (1934) (The war power “is a power to wage war successfully, and thus it permits the harnessing of the entire energies of the people in a supreme cooperative effort to preserve the nation. But even the war power does not remove constitutional limitations safeguarding essential liberties”). Likewise, we have made clear that, unless Congress acts to suspend it, the Great Writ of habeas corpus allows the Judicial Branch to play a necessary role in maintaining this delicate balance of governance, serving as an important judicial check on the Executive’s discretion in the realm of detentions. See St. Cyr, 533 U. S., at 301 (“At its historical core, the writ of habeas corpus has served as a means of reviewing the legality of Executive detention, and it is in that context that its protections have been strongest”). Thus, while we do not question that our due process assessment must pay keen attention to the particular burdens faced by the Executive in the context of military action, it would turn our system of checks and balances on its head to suggest that a citizen could not make his way to court with a challenge to the factual basis for his detention by his government, simply because the Executive opposes making available such a challenge. Absent suspension of the writ by Congress, a citizen detained as an enemy combatant is entitled to this process.

Because we conclude that due process demands some system for a citizen detainee to refute his classification, the proposed “some evidence” standard is inadequate. Any process in which the Executive’s factual assertions go wholly unchallenged or are simply presumed correct without any opportunity for the alleged combatant to demonstrate otherwise falls constitutionally short. As the Government itself has recognized, we have utilized the “some evidence” standard in the past as a standard of review, not as a standard of proof. Brief for Respondents 35. That is, it primarily has been employed by courts in examining an administrative record developed after an adversarial proceeding—one with process at least of the sort that we today hold is constitutionally mandated in the citizen enemy-combatant setting. See, e.g., St. Cyr, supra; Hill, 472 U. S., at 455–457. This standard therefore is ill suited to the situation in which a habeas petitioner has received no prior proceedings before any tribunal and had no prior opportunity to rebut the Executive’s factual assertions before a neutral decisionmaker.

Today we are faced only with such a case. Aside from unspecified “screening” processes, Brief for Respondents 3–4, and military interrogations in which the Government suggests Hamdi could have contested his classification, Tr. of Oral Arg. 40, 42, Hamdi has received no process. An interrogation by one’s captor, however effective an intelligence-gathering tool, hardly constitutes a constitutionally adequate factfinding before a neutral decisionmaker. Compare Brief for Respondents 42–43 (discussing the “secure interrogation environment,” and noting that military interrogations require a controlled “interrogation dynamic” and “a relationship of trust and dependency” and are “a critical source” of “timely and effective intelligence”) with Concrete Pipe, 508 U. S., at 617–618 (“one is entitled as a matter of due process of law to an adjudicator who is not in a situation which would offer a possible temptation to the average man as a judge… which might lead him not to hold the balance nice, clear and true” (internal quotation marks omitted). That even purportedly fair adjudicators “are disqualified by their interest in the controversy to be decided is, of course, the general rule.” Tumey v. Ohio, 273 U. S. 510, 522 (1927). Plainly, the “process” Hamdi has received is not that to which he is entitled under the Due Process Clause.

There remains the possibility that the standards we have articulated could be met by an appropriately authorized and properly constituted military tribunal. Indeed, it is notable that military regulations already provide for such process in related instances, dictating that tribunals be made available to determine the status of enemy detainees who assert prisoner-of-war status under the Geneva Convention. See Enemy Prisoners of War, Retained Personnel, Civilian Internees and Other Detainees, Army Regulation 190–8, §1–6 (1997). In the absence of such process, however, a court that receives a petition for a writ of habeas corpus from an alleged enemy combatant must itself ensure that the minimum requirements of due process are achieved. Both courts below recognized as much, focusing their energies on the question of whether Hamdi was due an opportunity to rebut the Government’s case against him. The Government, too, proceeded on this assumption, presenting its affidavit and then seeking that it be evaluated under a deferential standard of review based on burdens that it alleged would accompany any greater process. As we have discussed, a habeas court in a case such as this may accept affidavit evidence like that contained in the Mobbs Declaration, so long as it also permits the alleged combatant to present his own factual case to rebut the Government’s return. We anticipate that a District Court would proceed with the caution that we have indicated is necessary in this setting, engaging in a factfinding process that is both prudent and incremental. We have no reason to doubt that courts faced with these sensitive matters will pay proper heed both to the matters of national security that might arise in an individual case and to the constitutional limitations safeguarding essential liberties that remain vibrant even in times of security concerns.

IV
Hamdi asks us to hold that the Fourth Circuit also erred by denying him immediate access to counsel upon his detention and by disposing of the case without permitting him to meet with an attorney. Brief for Petitioners 19. Since our grant of certiorari in this case, Hamdi has been appointed counsel, with whom he has met for consultation purposes on several occasions, and with whom he is now being granted unmonitored meetings. He unquestionably has the right to access to counsel in connection with the proceedings on remand. No further consideration of this issue is necessary at this stage of the case.

* * *

The judgment of the United States Court of Appeals for the Fourth Circuit is vacated, and the case is remanded for further proceedings.

It is so ordered.

Notes
Footnote 1

Here the basis asserted for detention by the military is that Hamdi was carrying a weapon against American troops on a foreign battlefield; that is, that he was an enemy combatant. The legal category of enemy combatant has not been elaborated upon in great detail. The permissible bounds of the category will be defined by the lower courts as subsequent cases are presented to them.

Footnote 2

Because we hold that Hamdi is constitutionally entitled to the process described above, we need not address at this time whether any treaty guarantees him similar access to a tribunal for a determination of his status.