delivered the opinion of the Court.
The issue before us is ah important one for the people of our country and their Government. It involves the delicate question of the President’s power, acting through the Attorney General, to authorize electronic surveillance in internal security matters without prior judicial approval. Successive.Presidents for more, than one-quarter of a century have authorized such surveillance in varying degrees,1 without guidance from the Congress or a definitive decision of this Court.. This case brings the issue here for the first time. Its resolution is a matter of national concern, requiring sensitivity both to the Government’s right to protect itself from unlawful subversion and attack and to the citizen’s right to be secure in his privacy against unreasonable Government intrusion.
This case arises from a criminal proceeding in the United States District Court for the Eastern District of Michigan, in which the United States charged three defendants with conspiracy to destroy Government property in violation of 18 U. S. C. § 371. One of the defendants, Plamondon, was charged with the dynamite bombing of an office of the Central Intelligence Agency in Ann Arbor, Michigan.
During pretrial proceedings, the defendants moved to compel the United States to disclose certain electronic *300surveillance information and to conduct a hearing to determine whether this information “tainted” the evidence on which the indictment was based or which theGovernment intended to offer at trial. In response, the- Government filed an affidavit of the Attorney General, acknowledging that its agents had overheard conversations in which Plamondon had participated. The affidavit also stated that the Attorney General approved the wiretaps “to gather intelligence information deemed necessary to protect the nation from attempts of domestic organizations to attack and subvert the existing structure of the Government.” 2 The logs of the surveillance *301were filed in a sealed exhibit for in camera, inspection by the District Court. •
On the basis of the Attorney General’s affidavit and the sealed exhibit, the' Government' asserted that the surveillance was lawful, though conducted without prior judicial approval, as a reasonable exercise of- the President’s power (exercised through the Attorney General) to protect the national security. The District Court held that the surveillance violated the Fourth . Amendment, and ordered the Government to 'make full, disclosure to Plamondon of his overheard conversations. 321 F. Supp. 1074 (ED Mich. 1971).
The Government then filed in the Court of Appeals for the Sixth Circuit a petition for-a writ of mandamus to set aside the District Court order, which was stayed pending final disposition of the case. ..After- concluding that it had jurisdiction,3 that ‘court held that the surveillance was unlawful and that the District Court had properly .required disclosure of the overheard conversations, 444 F. 2d 651 (1971). We granted certiorari, 403 U. S. 930.
I
Title III of the Omnibus Crime Control and Safe Streets Act, 18 U. S. C. §§ 2510-2520, authorizes the use of electronic surveillance for classes of crimes care*302fully specified in 18 U. S. C. § 2516. Such surveillance is subject to prior court order. Section 2518 sets forth the detailed and particularized application necessary to obtain such an order as well as carefully circumscribed conditions for its use. The Act represents a comprehensive attempt by Congress to promote more effective control of crime while protecting the privacy of individual thought and expression. Much of Title III was drawn to meet the constitutional requirements for electronic surveillance enunciated by this Court in Berger v. New York, 388 U. S. 41 (1967), and Katz v. United States, 389 U. S. 347 (1967).
Together with the elaborate surveillance requirements in Title III, there is the following proviso; 18 U. S. C. §2511(3):
“Nothing contained in this chapter or in section 605 of the Communications Act of 1934 (48 Stat. 1143; 47 U. S. C. 605) shall limit the constitutional power of the President to take such measures as he deems necessary to protect the Nation against actual or potential attack or other hostile acts of a foreign power, to obtain foreign' intelligence information deemed essential to the security of the United States, or to protect national security information against foreign intelligence activities. Nor shall anything contained in this chapter he deemed to limit the constitutional power, of the President to take such measures as he deems necessary to protect the United States against the overthrow of the Government by force or other unlawful means, or against any other clear and present danger to the structure or existence of the Government. The contents of any wire or oral communication intercepted by authority of the President in the exercise of the foregoing powers may be received in evidence in any trial hearing, *303or other proceeding only where such interception was reasonable, and shall not be otherwise used or disclosed except as is necessary to implement that power.” (Emphasis supplied.)
The Government relies on § 2511 (3). It argues that “in excepting national security surveillances from the Act’s warrant requirement. Congress recognized the President’s authority to conduct such, surveillances without prior, judicial approval.” Brief for United States 7, 28. The section thus is viewed as a recognition or affirmance of a constitutional authority in the President to conduct warrantless domestic security surveillance such as that involved in this case.
We think the language of § 2511 (3), as well as the legislative history of the statute, refutes this-interpretation. . The relevant language is that:
“Nothing contained in this chapter . . . shall limit the constitutional power of the President to take such measures ás he deems necessary to protect.. .”
against the dangers specified. At most, this is an implicit recognition that the President does have certain powers in the specified areas. Few would doubt this, as the section refers — among other things — to protection “against actual or potential attack or other hostile acts of a foreign power.” But so far as the use of the President’s electronic surveillance power is concerned, the language is essentially neutral.
Section 2511 (3) certainly confers no power, as the language is wholly inappropriate for such a purpose. It merely provides that the Act shall not be interpreted to limit or disturb such power as the President may have under the Constitution. In short, Congress simply left presidential powers where it found thém. This view is reinforced by the general context of Title III. Section 2511 (1) broadly prohibits the use of electronic *304surveillance “{ejxcept as otherwise specifically provided in this chapter.” Subsection (2) thereof contains four specific exceptions. In each of the specified exceptions, the statutory language is as follows:
“It shall not be unlawful ... to intercept” the particular type of communication described.4
The language of subsection (3), here involved, is to be contrasted with the language of the exceptions set forth in the preceding subsection. Rather than stating that warrantless presidential uses of electronic surveillance “shall not be unlawful” and thus employing the standard language of exception, subsection (3) merely disclaims any intention to “limit the constitutional power of the President.”
The express grant of authority to conduct surveil-lances is found in § 2516, which authorizes the Attorney General to make application to a federal judge when surveillance may provide evidence of certain offenses. These offenses are described with meticulous care and specificity.
Where the Act authorizes surveillance, the procedure to be followed is specified in §2518. Subsection (1) thereof requires application to a judge of competent jurisdiction for a prior order of approval, and states in detail the information réquired in such application.5 *305Subsection (3) prescribes the necessary eleménts of probable cause which the .judge must find before issuing an order authorizing an interception. Subsection (4) sets forth the required contents of such an order.. *306Subsection (5) sets strict time limits on an order. Provision is made in subsection (7) for “an emergency-situation” found to exist by the Attorney General (or by the principal prosecuting attorney of a State) “with respect to conspiratorial activities threatening the national security interest.” In such a situation, emergency surveillance may be conducted “if an application for an order approving the interception is made . . . within forty-eight hours.” If such an order is not obtained, or the application therefor is denied, the interception is deemed to be a violation of the Act.
In view of these and other interrelated provisions delineating permissible interceptions of particular criminal activity upon carefully specified conditions, it would have been incongruous for Congress to have legislated with respect to the important and complex area of national security in a single brief and nebulous paragraph. This would not comport with the sensitivity of the problem involved or with the extraordinary care Congress exercised in drafting other sections of the Act. We therefore think the conclusion inescapable that Congress only intended to make clear that the Act simply did not legislate with respect to national security surveillances.6
The legislative history of §2511(3) supports this interpretation. Most relevant is the colloquy between Senators Hart, Holland, and McClellan on the Senate floor:
“Mr.'HOLLAND. . .. The section [2511(3)] from which the Senator [Hart] has read does not affirma*307tively give any power. ... We are not affirmatively conferring any power upon the President. We are simply saying that nothing herein shall limit such power as the President has under the Constitution. . . . We certainly do not grant him a thing.
“There is nothing affirmative in this statement.
“Mr. McCLELLAN. Mr. President, we make it understood that we are not trying to take anything away from-him.
“Mr. HOLLAND. The Senator is correct.
“Mr. HART. Mr. President, there is no intention • here to expand by this language a constitutional power. Clearly we could not do so.
“Mr. McCLELLAN. Even though intended, we could not do so.
“Mr. HART. . . . However, we are agreed that this language should not be regarded as intending to grant any authority, including authority to put a bug on, that the President does not have now.
“In addition, Mr. President, as I think our exchange makes clear, nothing in section 2511 (3) even attempts to define the limits of the. President’s national security power under present law, which I have always found extremely vague .... .Section 2511(8) 'merely says that if the President has such a power, then its exercise is in no way affected by title III.” 7 (Emphasis supplied.)
*308One could hardly expect a clearer expression of congressional neutrality. The debate above explicitly indicates that nothing in § 2511 (3) was intended to expand or to contract or to define whatever presidential surveillance powers existed in matters affecting the national security. If we could accept the Government's characterization of § 2511 (3) as a congressionally prescribed exception to the general requirement of a warrant, it would be necessary to consider the question of whether the surveillance in this casé came within the exception and, if so, whether the statutory exception was itself constitutionally valid. But viewing § 2511 (3) as a congressional' disclaimer and expression of neutrality, we hold that the statute is not the measure of the executive authority asserted in this case. Rather, we must look to the constitutional powers of the President.
II
It is important at the outset to emphasize the limited nature of the question before the Court. This case raises- no constitutional challenge to electronic surveillance as specifically authorized by Title III of the Omnibus Crime Control and Safe Streets Act of 1968. Nor. is there any question or doubt as to the necessity of obtaining a warrant in the surveillance of crimes unrelated to the national security interest. Katz v. United States, 389 U. S. 347 (1967); Berger v. New York, 388 U. S. 41 (1967). Further, the instant case requires no judgment on the scope of the President's surveillance power with respect to the activities of foreign powers, within or without this country. The Attorney General’s affidavit in this case states that, the surveillances were *309“deemed, necessary to protect the nation from attempts of domestic organizations to attack and subvert the existing structure of Government” (emphasis supplied). There -is no evidence of any involvement, directly or indirectly, of a foreign power.8
Our present inquiry, though important, is therefore a narrow one. It addresses a question left open by. Katz, supra, at 358 n. 23:
“Whether safeguards othér than prior authorization by- a magistrate would satisfy the Fourth Amendment in a situation involving the national-security . . 7 .”
The determination of this question requires the essential Fourth .Amendment inquiry into .the “reasonableness” of the search and seizure in question, and the way in which that “reasonableness” derives content and mean*310ing through reference to the warrant ulause. Coolidge v. New Hampshire, 403 U. S. 443, 473-84 (1971).
We begin the inquiry by noting that the President of the United States has the fundamental duty, under Art. II, § 1, of the Constitution, to “preserve, protect and defend the Constitution of the United States.” Implicit in that duty is the power to protect our Government against those who. would subvert or overthrow it by unlawful means. In the discharge of this duty, the President — through the Attorney General— may find it necessary to employ electronic surveillance to obtain intelligence information on the plans of those who plot unlawful acts against the Government.9 The use of such surveillance in internal security cases has been sanctioned more or less continuously by various Presidents and Attorneys General since July 1946.10 *311Herbert Brownell, Attorney General under President Eisenhower, urged the use of electronic surveillance both in internal and international security matters on the grounds that those acting against the Government
“turn to the telephone to carry on their intrigue. The success of their plans frequently rests upon piecing together shreds of information received from many sources and many- nests. The participants in the conspiracy are often dispersed and stationed in various strategic positions in government and industry throughout the country.”11
Though the Government and respondents debate their seriousness and magnitude, threats and acts of sabotage against the Government exist in sufficent number to justify investigative powers with respect to them.12 The covertness and complexity of potential unlawful con*312duct against the Government and the necessary dependency of many conspirators upon the telephone make electronic surveillance an effective investigatory instrument in certain circumstances. The marked acceleration in technological developments and sophistication in their use have resulted in new techniques for the planning, commission, and concealment of criminal activities. It would be contrary to the public interest for Government to deny to itself the prudent and lawful employment of those very techniques which are employed against the Government and its law-abiding citizens.
It has been said that “[t]he most basic' function of any government is to provide for the security of the individual and of his property.” Miranda v. Arizona, 384 U. S. 436, 539 (1966) (White, J., dissenting). And unless Government safeguards its own capacity to function and to preserve the security of its people, society itself could become so disordered that all rights' and liberties would be endangered. As Chief Justice Hughes reminded us in Cox v. New Hampshire, 312 U. S. 569, 574 (1941):
“Civil liberties, as guaranteed by the Constitution, imply the existence of an organized society maintaining public order without which liberty itself would be lost in the excesses of unrestrained' abuses.”
But a recognition of these elementary truths does not make the employment by Government of electronic surveillance a welcome development — even when employed with restraint' and under judicial supervision. There is, understandably, a deep-seated uneasiness and apprehension that this capability will be used to intrude upon cherished privacy of law-abiding citizens.13 We *313look to the Bill of Rights to safeguard this privacy. Though physical entry of the home is the chief evil against which the wording of the Fourth Amendment is directed, its broader spirit, now shields private speech from unreasonable surveillance. Katz v. United States, supra; Berger v. New York, supra; Silverman v. United States, 365 U. S. 505 (1961). Our decision in Katz refused to lock the Fourth Amendment into • instances of actual physical trespass. Rather, the Amendment governs “not only the seizure of tangible items, but extends'as well to the recording of oral statements . . . without any ‘technical trespass under . . . local property law.’ ” Katz, supra, at 353. That decision implicitly recognized that the broad and unsuspected governmental incursions into conversational privacy which electronic surveillance entails14 necessitate the application of Fourth Amendment safeguards.
National security cases, moreover, often reflect a convergence of First and Fourth Amendment values not present in cases of “ordinary” crime. Though the investigative duty of the executive may be stronger in such cases, so also is there greater jeopardy to constitutionally protected speech. “Historically the struggle for freedom of speech and press in England was bound up with the issue of the scope of the search and seizure *314power,” Marcus v. Search Warrant, 367 U. S. 717, 724 (1961). History abundantly documents the tendency of Government — however benevolent and benign its motives — to view with suspicion those who most fervently dispute its policies. Fourth Amendment protections become the more necessary when the targets of official surveillance may be those suspected of unorthodoxy in their political beliefs. The danger to political dissent is acute where the Government attempts to act under so vague a concept as the power to protect “domestic security.” Given the difficulty of defining the domestic security, interest, the danger of abuse in acting to protect that interest becomes apparent. Senator Hart addressed this dilemma in the floor debate on § 2511 (3):
“As I read it — and this is my fear — we are saying that the President, on his motion, could declare— name your favorite poison — draft dodgers, Black Muslims, the Ku Klux Klan, or civil rights activists to be a clear and present danger to. the structure or existence of the Government.” 15
The price of lawful public dissent must not be a dread of subjection to an unchecked surveillance power. Nor must the fear of unauthorized official eavesdropping deter vigorous citizen.dissent and discussion of Government action in private conversation. For private dissent, no less than open public discourse, is essential to our free society.
Ill
As the Fourth Amendment is not absolute in its terms, our task is to examine and balance the basic values at stake in this case: the duty of Government *315to protect the domestic security, and the potential danger posed by unreasonable surveillance to individual privacy and free expression. If the legitimate need of Government to. safeguard domestic security requires the use of electronic surveillance, the question is whether the needs of citizens for privacy and free expression may not be better protected by requiring a warrant before such surveillance, is undertaken; We must also ask whether a warrant requirement would unduly frustrate; the. efforts of Government to protect itself from acts of subversion and overthrow, directed against it.
Though the Fourth Amendment speaks broadly of ‘unreasonable searches and seizures,” the definition of “reasonableness”' turns, at least in part, on the more specific commands of the warrant clarise. Some have argued that “[t]he relevant'.test is hot whether it is reasonable to procure á search warrant, but whethér the search was reasonable,”. United States v. Rabinowitz, 330 U. S. 56, 66 (1950).16 This view, however, overlooks the second clause of the Amendment. The warrant clause of the Fourth Amendment is not dead language. Rather, it has been.
“a valued part of our constitutional law for decades, and it has determined the result in scores and scores' of cases in courts all over this country. It is riot an inconvenience to be somehow ‘weighed’ against the claims of, police efficiency. It is, or should *316-be,- an- important working part of our machinery of government, operating as a matter of course to check the - ‘well-intentioned but mistakenly overzealous executive officers’. who are a part of any system of law enforcement.” Coolidge v. New Hampshire, 403 U. S., at 481.
See also United States v. Rabinowitz, supra, at 68 (Frankfurter, J.,, dissenting); Davis y. United States, 328 U. S. 582, 604 (1946) (Frankfurter, J., dissenting):
Over two centuries ago, Lord Mansfield held that common-law principles prohibited warrants that ordered the' arrest of unnamed individuals who the. officer might conclude were guilty, of seditious libel. “It is not fit,” . said Mansfield, “that the receiving. oi- judging of the. information should be left to the discretion of . the. officer. The magistrate ought to . judge;’ and should . give certain directions to the officer.” Leach v. Three of the King’s Messengers, 19 How. St. Tr. 1001, 1027 (1765).
• Lord Mansfield’s formulation touches' the very heart of the Fourth Amendment directive: that, where practical, a governmental search,and seizure should repre- ' sent both the efforts of the officer to gather evidence of .wrongful acts and the judgment of the magistrate that the collected evidence is sufficient to justify invasion of a citizen’s private premises or conversation.' Inherent in the concept of a warrant is its issúance by a “neutral and detached, magistrate.” Coolidge v. New Hampshire, supra, at 453; Katz v. United States, supra, at 356. The further requirement of “probable cause” instructs the magistrate that baseless searches shall not proceed.
These Fourth Amendment freedoms cannot properly be guaranteed if domestic security surveillances may be' conducted solely .within the discretion of the Execu*317tive Branch. The Fourth Amendment does not contemplate the executive officers of .Government as neutral and disinterested magistrates. . Their duty and responsibility are to enforce the- laws, to investigate, and to prosecute. Katz v. United States, supra, at 359-360 (Douglas, J., concurring). But those charged with this investigative and prosecutorial duty should not be the sole judges of when to utilize constitutionally sensitive means in pursuing their tasks. The historical judgment, which the Fourth Amendment accepts, is that unreviewed executive discretion may yield too. readily to pressures to-obtain incriminating evidence and overlook potential invasions of privacy and protected speech.17
It may well be that, in the instant case, the Government’s surveillance of Plamondon’s conversations was a reasonable one which readily would have gained prior judicial approval. But this Court “has never sustained a search upon the sole ground that officers reasonably expected to .find evidence of a particular crime and voluntarily confined their activities, to the least intru-. sive means consistent with that end.” Katz, supra, at 356-35.7. The Fourth Amendment contemplates a prior judicial judgment,18 not the risk that executive discretion may be reasonably exercised. This judicial role accords with our basic constitutional doctrine that individual freedoms will best be preserved through . a separation of powers and division of functions among the different branches and levels of Government. Harlan, Thoughts at a Dedication: Keeping the Judicial Function in Balance, 49 A. B. A. J. 943-944 (1963). The independent check upon executive discretion.is not *318satisfied, as the Government' argues, by “extremely limited” post-surveillance judicial review.19 Indeed, post-surveillance review would never reach the- surveillances which failed to result in prosecutions. Prior review by a neutral and detached' magistrate is the time-tested means of effectuating Fourth Amendment rights. Beck v. Ohio, 379 U. S. 89, 96 (1964).
It is true that there have been some exceptions to the warrant requirement. Chimel v. California, 395 U. S. 752 (1969); Terry v. Ohio, 392 U. S. 1 (1968); McDonald v. United States, 335 U. S. 451 (1948); Carroll v. United States, 267 U. S. 132 (1925). But those exceptions are few in number and carefully delineated, Katz, supra, at 357; in general, they serve the legitimate needs of law enforcement officers to protect their own well-being and preserve evidence from destruction. Even while carving out those exceptions, the Court has reaffirmed the principle that the “police must, whenever practicable, obtain advance judicial approval of searches and seizures through the warrant procedure,” Terry v. Ohio, supra, at 20; Chimel v. California, supra, at 762.
The Government argues that the special circumstances applicable to domestic, security, surveillances necessitate a further exception to the warrant requirement. It is urged that the requirement of prior judicial review would obstruct the President in the discharge of his constitutional duty to protect domestic, security. We are told further that these surveillances • are. directed- primarily to the collecting and maintaining of intelligence with *319respect to subversive forces/ and are not an attempt to gather evidence for specific criminal prosecutions. It is said that this type of surveillance should not be subject to traditional warrant requirements which were established to govern investigation' of criminal activity, not ongoing intelligence gathering. Brief for United States 15-16, 23-24; Reply Brief for United States 2-3.
The Government further insists that courts “as a practical matter would have neither-the knowledge nor the techniques necessary to determine whether there was probable cause to believe that surveillance was necessary to protect national security.”. These security problems, the Government contends, involve “a large number of complex and subtle factors” beyond the competence of courts to evaluate. Reply Brief for United States 4.
As a final reason for exemption from a warrant requirement, the Government believes that disclosure to a magistrate of all or even a significant portion of the information' involved in domestic security surveillances “would create serious potential dangers to -the national security and to the lives of informants and agents., . . .' Secrecy is the essential ingredient in intelligence gathering; requiring prior judicial authorization would create a greater 'danger of leaks . . . , because in addition to the judge, you have the clerk,-.the stenographer and some other officer like a law assistant or bailiff who may be apprised of the nature’ of the surveillance-.” Brief for United States 24-25:
These contentions in behalf .of a complete exemption from the warrant requirement, when urged on behalf of the President and the national security in -its domestic implications', merit the most careful consideration. We •certainly do not reject them lightly, especially at a time of worldwide ferment and when civil disorders in this country are more prevalent than iñ the less turbulent *320periods of our history.' There is, no doubt, pragmatic force to the Government’s position.
But we do not think a case has been made for the requested departure from Fourth Amendment standards. The circumstances, described do not justify complete exemption of domestic security surveillance from prior judicial scrutiny. Official surveillance, whether its purpose be criminal investigation or ongoing intelligence gathering, risks infringement of constitutionally protected privacy of speech. Security surveillances are especially sensitive because of the inherent vagueness of the domestic security concept, the necessarily broad and continuing nature of intelligence gathering, and the temptation to utilize such surveillances to oversee political dissent. We recognize, as we have before, the constitutional basis, of the President’s domestic security role, but we think it must be exercised in a manner compatible with the Fourth Amendment. In this case w;e hold that this requires an appropriate prior warrant procedure.
We cannot accept the Government’s argument that internal security matters are too. subtle and complex for judicial evaluation. Courts regularly deal with the most difficult issues of our society. There is no reason to believe that federal judges will be insensitive to or uncomprehending of the issues involved in domestic security cases. Certainly courts can recognize, that domestic security surveillance involves-different considerations from the surveillance of “ordinary crime.” If the threat is too subtle or complex for our senior law enforcement officers to convey its significance to a court, one may question whether there is probable cause for surveillance.
Nor do we believe prior judicial approval will fracture the secrecy essential to official intelligence gathering. The- investigation 'of criminal activity has long *321involved imparting , sensitive information to judicial officers who have respected the confidentialities involved. Judges may be counted upon to. be especially conscious of security requirements in national security cases. Titie III of the Omnibus Crime Control and Safe Streets Act already has imposed this responsibility on the judiciary in connection with such crimes as espionage, sabotage, and treason, .§§ 2516 (l.)(a) and (c), each of which may involve domestic as well as foreign security threats. Moreover, a warrant application involves no public or adversary proceedings: it is an ex parte request before a. magistrate or judge; Whatever security dangers clerical and secretarial personnel may pose can be minimized by proper administrative measures, possibly to the point of allowing the Government itself to provide the necessary clerical assistance.
Thus, we conclude that the Government’s concerns do not justify departure in this case from the customary Fourth Amendment requirement of judicial approval prior to initiation of a search or surveillance. Although some added burden will be imposed upon the Attorney General, this inconvenience is justified in a free society to protect constitutional values. Nor do we think the Government’s domestic surveillance powers will be impaired to any significant degree. A prior warrant establishes presumptive validity of the surveillance and will minimize the burden of justification in post-surveillance judicial review. By no means of least importance will be the reassurance of the public generally that indiscriminate wiretapping and bugging of law-abiding citizens cannot occur.
IV
We emphasize, before concluding this opinion, the scope of our decision. As stated at the outset, this case involves only the domestic aspects of national security. We have not addressed, and express no opinion *322as to, the issues which may be involved with respect to activities of foreign powers or their agents.20 Nor does our decision rest on thé langi^age of § 2511 (3) or any other section of Title III of the Omnibus Crime Control and Safe Streets Act of 1968. That Act does not attempt to define or delineate the powers of the President to meet domestic threats to the national security.
Moreover, we do not hold that the same type of standards and procedures prescribed by Title III are necessarily applicable to this case. , We recognize that domestic security surveillance may involve different policy and practical considerations from the surveillance of “ordinary crime.” The gathering of security intelligence is often long range and involves the interrelation of various sources and types of information. The exact targets of such surveillance may be more difficult to identify than in surveillance operations against many types of crime specified in Title III. Often, too, the emphasis of domestic intelligence gathering is on the prevention of unlawful activity or the enhancement of the Government’s preparedness for some possible future crisis or emergency. Thus, the focus of domestic surveillance may be less precise than that directed against more conventional types of crime.
Given these potential distinctions between Title III criminal surveillances and those involving the domestic security, Congress may wish to. consider protective standards for the latter , which differ from those already prescribed for specified crimes in Title III. Different standards may be compatible with the Fourth Amend*323ment if they are reasonable both in relation to the legitimate need of Government for intelligence information and the protected rights of our citizens. For the warrant application may vary according to the governmental interest to be enforced and the nature of citizen rights deserving protection. As the 'Court said in Camara v. Municipal Court, 387 U. S. 523, 534-535 (1967):
“In cases in which the Fourth Amendment requires that a warrant to search be. obtained, ‘probable cause’ is the standard by which a particular decision -to search is tested against the constitutional mandate of reasonableness. . . . In determining whether a particular inspection is reasonable — -and thus in determining whether there is probable cause to issue a warrant for that inspection — the need for. the inspection must be weighed in terms of these reasonable goals of code enforcement.”
It may be that’ Congress, for example, would judge that the application and affidavit showing probable cause need. not follow the exact requirements of § 2518 but should allege other circumstances more appropriate to domestic security cases; that the request for prior court •authorization could, in sensitive cases, be made to. any member of a specially designated court (e. g., the District Court for the District of Columbia or the Court of Appeals for the District of Columbia Circuit); and that the time and reporting requirements need not be so strict as those in § 2518. ■
The above paragraph does not, -of course, attempt to guide the congressional judgment but rather to delineate the present scope of our own opinion. We do not attempt to detail the precise standards for domestic secu-. rity warrants any more than our decision in Katz sought to set the refined requirements for the specified criminal surveillances which now constitute Title III. We do *324hold, however, that prior judicial approval is required for the type .of domestic security surveillance involved in this case and that such approval may be made in accordance with such reasonable standards as the Congress may prescribe.
V
As the surveillance of Plamondon’s conversations was unlawful, because conducted without prior judicial approval, the courts below correctly held that Alderman v. United States, 394 U. S. 165 (1969), is controlling and that it requires disclosure to the accused of his own im-permissibly intercepted conversations. As stated in Alderman, “the trial court .can and should, where appropriate, place a defendant and his counsel under enforceable orders against unwarranted disclosure of thé materials which they may be entitled to inspect.” 394 U. S., at 185.21
The judgment of the Court of Appeals is hereby
Affirmed.
The Chief Justice concurs in the result. Mr, Justice Rehnquist took no part in the consideration or decision of this case.See n. 10, infra.
The Attorney General’s affidavit reads as follows:
“JohN N. Mitchell being duly sworn deposes and says:
“1. I ani the Attorney General of the United States.
“2. This affidavit is submitted in connection with the Government’s opposition to the disclosure to the defendant Plamondon of information concerning the overhearing of his conversations which occurred during the course of eléctronic surveillances which the Government contends were legal.
“3. The defendant Plamondon has participated in conversations which were overheard by Government agents who were monitoring wiretaps' which were being employed to gather intelligence information deemed necessary to protect the nation from attempts of domestic organizations to attack and subvert the existing structure of the Government. The records of the Department of Justice. reflect the installation of these' wiretaps had been expressly approved by the Attorney General. '
“4. Submitted with this affidavit is a sealed exhibit containing the records of the intercepted conversations, a description of the premises that were the subjects of surveillances, and copies of the memoranda reflecting the Attorney General’s express approval of the installation of the surveillances.
“5. I certify that it would prejudice the national interest to disclose the particular facts concerning these surveillances other than to the court in camera. Accordingly, the sealed exhibit referred to herein is being submitted solely for the court’s in camera inspection and a copy of the sealed exhibit is not being furnished to the defendants. I would request, the court, at the conclusion of its *301hearing on this matter,- to place the sealed exhibit in a sealed envelope and return it to the Department of Justice where it will be retained under seal so that it may be submitted to any appellate court that may review this matter.”
Jurisdiction was challenged before the Court of Appeals on the ground that the District Court’s order was interlocutory and not appealable under 28 U. S. C. § 1291. On this issue, the court correctly held that it did have jurisdiction, relying upon the All Writs Act, 28 U. S. C. § 1651, and cases cited in its opinion, 444 F. 2d, at 655-656. No attack was made in this Court as to the appropriateness of the writ of mandamus procedure.
These exceptions relate to certain activities of communication common carriers and the Federal Communications Commission, and to specified situations where a party to the communication has consented to the interception.
Title 18 U. S. C. §2518, subsection (1), reads as follows:
“§ 2518. Procedure for interception of wire or oral communications “(1) Each application for an order authorizing or approving the interception of a wire or oral communication shall be made in writing upon oath or affirmation to a judge of competent jurisdiction *305and shall state the applicant’s authority to' make such application. Each application shall include the following information:
“(a) the identity of the investigative or law enforcement officer making the application, and the officer authorizing the application;
“(b) a full and complete statement of the facts and circumstances relied upon by the applicant, to jústify his belief that an order should be issued, including (i) details as to the particular offense that has been, is being, or is about to be committed,' (ii) a particular description of the nature and location of the facilities from which or the place where the communication is to be intercepted, (in) a particular description of the type of communications sought to be intercepted, (iv) the identity of the person, if known, committing the offense and whose communications áre to be intercepted;
“(c) a full and complete statement as to whether or not other investigative procedures have been tried and failed or why they reasonably appear to be unlikely to succeed if tried or to be too dangerous;
“(d) a statement of the period of time for which the interception is required to be maintained. If the nature of the investigation is such that the authorization for interception should not automatically terminate when the described type of communication has been first obtained, a particular description of facts establishing probable cause' to believe that additional communications of the same type will occur thereafter;.
“(e) a full .and complete statement of the .facts concerning all previous applications known to the individual authorizing and making the application, made to any judge for authorization to intercept, or for approval of interceptions of, wire or oral communications involving any of the same persons, facilities or places specified in the application, and the action taken by the judge, on each such application; and
“(f) where the application .is for the extension- of an order, a statement setting forth the results thus far obtained from the interception, or a reasonable explanation of the failure to obtain such results.”
The final sentence of § 2511 (3) states that the contents of an interception “by authority of the; President in the exercise of the foregoing powers may be received in evidence . . . only where such interception was reasonable . . . This sentence seems intended to assure that when the President conducts lawful surveillance— pursuant to whatever power he may possess — the evidence is admissible.
114 Cong. Rec. 14751. Senator McClellan was the sponsor of the bill.. The above exchange constitutes the only time that § 2511 (3) was expressly debated on the Senate or House floor. The Report of the Senate Judiciary Committee is not so explicit as the exchange •on the floor, but it appears to recognize that under. § 2511 (3) the • national security power of the President — whatever it may be — “is not to be deemed disturbed.” S. Rep. No. 109.7, 90th Cong., 2d Sess., 94 (1968). See also The “National Security Wiretap”: Presidential Prerogative or Judicial Responsibility, where the author concludes that in § 2511 (3) “Congress took what amounted to a position of *308neutral noninterference on the question of the constitutionality of warrantless national security wiretaps authorized by the President.” 45 S. Cal. L. Rev. 888, 889 (1972).
Section 2511 (3) refers to “the constitutional power of the President” in two types of situations: (i) where necessary to protect against attack, other hostile acts or intelligence activities of a “foreign power”; or (ii) where necessary to protect against the overthrow of the' Government or other clear and present danger to the structure or existence of the Government. Although both of the specified situations are sometimes referred to as “national security” threats, the term “national security”- is used only in the first sentence of § 2511 (3) with respect to the activities of foreign powers. This case involves only the second sentence of §2511 (3), with' the threat emanating — according to the Attorney General’s affidavit — from “domestic organizations.” Although we attempt no precise definition, we use the term “domestic organization” in this opinion to mean a group or organization (whether formally or informally constituted) composed of citizens of the United States and which has no significant connection with a foreign power, its agents or agencies. No doubt there are cases where it will be difficult to distinguish between “domestic” and “foreign” unlawful activities directed against the Government of the United States where there is collaboration in varying degrees between domestic groups or organizations and agents or agencies of foreign powers. But this is not such a case.
Enactment of Title III reflects congressional recognition of the importance of such surveillance in combatting various types of crime. Frank S. Hogan, District Attorney for New York County for over 25 years, described telephonic interception, pursuant to court order, as “the single , most valuable weapon in law enforcement’s fight against organized crime.” 117 Cong. Rec. 14051. The “Crime Commission” appointed by President Johnson noted that “[t]he .great majority of law enforcement officials .believe that the evidence necessary to bring criminal sanctions to bear consistently on the higher echelons of organized crime will not be obtained without the aid of electronic surveillance techniques. They maintain these techniques are indispensable to develop adequate strategic intelligence concerning organized crime, to set up specific investigations, to.develop witnesses, to corroborate their testimony, and to serve as substitutes for them — each a necessary step in the evidence-gathering process'in organized crime investigations and prosecutions.” Report by the President’s Commission on Law Enforcement and Administration of Justice, The Challenge of Crime in a Free Society 201 (1967).
In that month Attorney General Tom Clark advised President Truman of the necessity of using wiretaps “in cases vitally affecting the domestic security.” In May 1940 President Roosevelt had au*311thorized Attorney General Jackson to utilize wiretapping in matters “involving the defense of the nation,” but it is questionable whether this language was meant to apply to solely domestic subversion. The nature and extent of wiretapping apparently varied under different administrations and Attorneys General, but, except for the sharp curtailment under Attorney General Ramsey Clark in the latter years of the Johnson administration, electronic surveillance has been used both against organized crime and in domestic security cases at least since .the 1946 memorandum from Clark to Truman. Brief for United States 16-18; Brief for Respondents 51-56; 117 Cong. Rec. 14056.
Brownell, The Public Security and Wire Tapping, 39 Cornell L. Q. 195, 202 (1954). See also Rogers, The Case For Wire Tapping, 63 Yale L. J. 792 (1954). •
The Government asserts that there , were 1,562 bombing incidents in the United States from January 1, 1971,’ to July 1, 1971, most of-which involved Government related facilities. Respondents dispute these statistics as incorporating many frivolous incidents as well as bombings against nongovernmental facilities. The precise level of this activity, however, is not relevant to the disposition of this case. Brief for United States 18; Brief for Respondents 26-29; Reply Brief for United States 13.
Professor Alan Westin has written on. the likely course of future conflict between the value of privacy and the “new technology” of law enforcement. Much of the book details techniques *313of physical and electronic surveillance and such possible- threats to personal privacy as psychological and personality testing and electronic information storage and retrieval. Not all of the contemporary threats to privacy emanate directly from the pressures of crime control. Privacy and Freedom (1967).
Though the total number of intercepts authorized by. state and federal judges pursuant to Tit. Ill of the. 1968 Omnibus Crime Control and Safe Streets Act was 597 in 1970, éaeh surveillance may involve interception of hundreds of different conversations. The average intercept in 1970 involved 44 people and 655 conversations, of which 295 or 45% were incriminating. 117 Cong. Rec. 14052.
114 Cong. Rec. 14750. The subsequent, assurances, quoted in part I of the opinion, that §2511 (3) implied no statutory grant, contraction, or definition of presidential power eased the Senator’s misgivings.
This view has not been accepted.' ’ In Chimel v. California, 395 U. S. 752 (1969), the Court considered the Government’s contention that the search be judged on a general “reasonableness” standard without reference to the warrant clause. .The Court concluded that argument was “founded on little more than a subjective view regarding the acceptability of certain, sorts of police conduct, and not on considerations relevant to Fourth Amendment interests. Under such, an unconfined analysis, Fourth Amendment protection in this area would approach the evaporation point.” Id., at 764-765.
N. Lasson, The History and Development of the Fourth Amendment to the United States Constitution 79-105 (1937).
We use the word “judicial” to connote the traditional Fourth Amendment requirement of a neutral and detached magistrate.
The Government.argues that domestic security wiretaps should be upheld by courts in post-surveillance review “[u]nless it appears that the Attorney General’s determination that the proposed surveillance relates to a national security'matter is arbitrary and capricious, i. e., that it constitutes a clear abuse of the broad discretion that the Attorney General has to obtain all information that will be helpful to the President in protecting the-Government .,. .” against the various unlawful acts in §2511(3). Brief for United States 22.
See n. 8, swgra.. For the view that warrantless surveillance, though impermissible in domestic security cases, may be constitutional where foreign powers are involved, see United States v. Smith, 321 F. Supp. 424, 425-426 (CD Cal. 1971); and American Bar Association Project on Standards for Criminal Justice, Electronic Surveillance 120, 121 (Approved. Draft 1971, and Feb. 1971 Supp. 11). See also United States v. Clay, 430 F. 2d 165 (CA5 1970).
We think it unnecessary at this time and on the facts , of this case to consider the arguments advanced by the Government for a re-examination of the basis and scope of the Court’s decision in Alderman.