*229OPINION
This is a review by certiorari of a conviction under 2 U. S. C. §192 for “contempt of Congress.” The misdemeanor is alleged to have been committed during a hearing before a congressional investigating committee. It is not the case of a truculent or contumacious witness who refuses to answer all questions or who, by boisterous or discourteous conduct, disturbs the decorum of the committee room. Petitioner was *230prosecuted for refusing to make certain disclosures which he asserted to be beyond the authority of the committee to demand. The controversy thus rests upon fundamental principles of the power of the Congress and the limitations upon that power. We approach the questions presented with conscious awareness of the far-reaching ramifications that can follow from a decision of this nature.
On April 29, 1954, petitioner appeared as a witness in compliance with a subpoena issued by a Subcommittee of the Committee on Un-American Activities of the House of Representatives. The Subcommittee elicited from petitioner a description of his background in labor union activities. He had been an employee of the International Harvester Company between 1935 and 1953. During the last eleven of those years, he had been on leave of absence to serve as an official of the Farm Equipment Workers International Union, later merged into the United Electrical, Radio and Machine Workers. He rose to the position of President of District No. 2 of the Farm Equipment Workers, a district defined geographically to include generally Canton and Rock Falls, Illinois, and Dubuque, Iowa. In 1953, petitioner joined the United Auto Workers International Union as a labor organizer.
Petitioner’s name had been mentioned by two witnesses who testified before the Committee at prior hearings. In September 1952, one Donald O. Spencer admitted having been a Communist from 1943 to 1946. He declared that he had been recruited into the Party with the endorsement and prior approval of petitioner, whom he identified as the then District Vice-President of the Farm Equipment Workers.1 Spencer also mentioned that petitioner had attended meetings at which only card-carrying Communists were admitted. A month before petitioner testified, one Walter Rumsey stated that he had been recruited into the Party by petitioner.2 Rumsey added that he had paid Party dues to and later collected dues from petitioner, who had assumed the name, Sam Brown. Rumsey told the Committee that he left the Party in 1944.
Petitioner answered these allegations freely and without reservation. His attitude toward the inquiry is clearly revealed from the statement he made when the questioning turned to the subject of his past conduct, associations and predilections:
“I am not now nor have I ever been a card-carrying member of the Communist Party. Rumsey was wrong when he said I had recruited him into the party, that I had received his dues, that I paid dues to him, and that I had used the alias Sam Brown.
“Spencer was wrong when he termed any meetings which I attended as closed Communist Party meetings.
“I would like to make it clear that for a period of time from approxi*231mately 1942 to 1947 I cooperated with the Communist Party and participated in Communist activities to such a degree that some persons may honestly believe that I was a member of the party.
“I have made contributions upon occasions to Communist causes. I have signed petitions for Communist causes. I attended caucuses at an FE convention at which Communist Party officials were present.
“Since I freely cooperated with the Communist Party I have no motive for making the distinction between cooperation and membership except the simple fact that it is the truth. I never carried a Communist Party card. I never accepted discipline and indeed on several occasions I opposed their position.
“In a special convention held in the summer of 1947 I led the fight for compliance with the Taft-Hartley Act by the FE-CIO International Union. This fight became so bitter that it ended any possibility of future cooperation.”3
The character of petitioner’s testimony on these matters can perhaps best be summarized by the Government’s own appraisal in its brief:
“A more complete and candid statement of his past political associations and activities (treating the Communist Party for present purposes as a mere political party) can hardly be imagined. Petitioner certainly was not attempting to conceal or withhold from the Committee his own past political associations, predilections, and preferences. Furthermore, petitioner told the Committee that he was entirely willing to identify for the Committee, and answer any questions it might have concerning, ‘those persons whom I knew to be members of the Communist Party,’ provided that, ‘to [his] best knowledge and belief,’ they still were members of the Party . . . .”4
The Subcommittee, too, was apparently satisfied with petitioner’s disclosures. After some further discussion elaborating on the statement, counsel for the Committee turned to another aspect of Rumsey’s testimony. Rumsey had identified a group of persons whom he had known as members of the Communist Party, and counsel began to read this list of names to petitioner. Petitioner stated that he did not know several of the persons. Of those whom he did know, he refused to tell whether he knew them to have been members of the Communist Party. He explained to the Subcommittee why he took such a position:
“I am not going to plead the fifth amendment, but I refuse to answer certain questions that I believe are outside the proper scope of your committee’s activities. I will answer any questions which this committee puts to me about myself. I will also answer questions about those persons whom I knew to be members of the Communist Party and whom I believe still are. I will not, however, answer any questions with respect to others with whom I associated in the past. I do not believe that any law in this country requires me to testify about persons who may in the past have been Communist Party members or otherwise engaged in Com*232munist Party activity but who to my best knowledge and belief have long since removed themselves from the Communist movement.
“I do not believe that such questions are relevant to the work of this committee nor do I believe that this committee has the right to undertake the public exposure of persons because of their past activities. I may be wrong, and the committee may have this power, but until and unless a court of law so holds and directs me to answer, I most firmly refuse to discuss the political activities of my past associates.”5
The Chairman of the Committee submitted a report of petitioner’s refusal to answer questions to the House of Representatives. H. R. Rep. No. 1579, 83d Cong., 2d Sess. The House directed the Speaker to certify the Committee’s report to the United States Attorney for initiation of criminal prosecution. H. Res. 534, 83d Cong., 2d Sess.6 A seven-count indictment was returned.7 Petitioner waved his right to jury trial and was found guilty on all counts by the court. The sentence, a fine of $100 and one year in prison, was suspended, and petitioner was placed on probation.
An appeal was taken to the Court of Appeals for the District of Columbia. The conviction was reversed by a three-judge panel, one member dissenting. Upon rehearing en banc, the full bench affirmed the conviction with the judges of the original majority in dissent. We granted certiorari because of the very important questions of constitutional law presented. 352 U. S. 822.
We start with several basic premises on which there is general agreement. The power of the Congress to conduct investigations is inherent in the legislative process. That power is broad. It encompasses inquiries concerning the administration of existing laws as well as proposed or possibly needed statutes. It includes surveys of defects in our social, economic or political system for the purpose of enabling the Congress *233to remedy them. It comprehends probes into departments of the Federal Government to expose corruption, inefficiency or waste. But broad as is this power of inquiry, it is not unlimited. There is no general authority to expose the private affairs of individuals without justification in terms of the functions of the Congress. This was freely conceded by the Solicitor General in his argument of this case.8 Nor is the Congress a law enforcement or trial agency. These are functions of the executive and judicial departments of government. No inquiry is an end in itself; it must be related to and in furtherance of a legitimate task of the Congress. Investigations conducted solely for the personal aggrandizement of the investigators or to “punish” those investigated are indefensible.
It is unquestionably the duty of all citizens to cooperate with the Congress in its efforts to obtain the facts needed for intelligent legislative action. It is their unremitting obligation to respond to subpoenas, to respect the dignity of the Congress and its committees and to testify fully with respect to matters within the province of proper investigation. This, of course, assumes that the constitutional rights of winesses will be respected by the Congress as they are in a court of justice. The Bill of Rights is applicable to investigations as to all forms of governmental action. Witnesses cannot be compelled to give evidence against themselves. They cannot be subjected to unreasonable search and seizure. Nor can the First Amendment freedoms of speech, press, religion, or political belief and association be abridged.
The rudiments of the power to punish for “contempt of Congress” come to us from the pages of English history. The origin of privileges and contempts extends back into the period of the emergence of Parliament. The establishment of a legislative body which could challenge the absolute power of the monarch is a long and bitter story. In that struggle, Parliament made broad and varied use of the contempt power. Almost from the beginning, both the House of Commons and the House of Lords claimed absolute and plenary authority over their privileges. This was an independent body of law, described by Coke as lex parlia-menti.9 Only Parliament could declare what those privileges were or what new privileges were occasioned, and only Parliament could judge what conduct constituted a breach of privilege.
In particular, this exclusion of lex parliament! from the lex tarrae, or law of the land, precluded judicial review of the exercise- of the contempt power or the assertion of privilege, Parliament declared that no court had jurisdiction to consider such questions. In the latter part of the seventeenth century, an action for false imprisonment was brought by one Jay who had been held in contempt. The defendant the Serjeant-at-Arms of the House of Commons, demurred that he had taken the *234plaintiff into custody for breach of privilege. The Chief Justice, Pember-ton, overruled the demurrer. Summoned to the bar of the House, the Chief Justice explained that he believed that the assertion of privilege went to the merits of the action and did not preclude jurisdiction. For his audacity, the Chief Justice was dispatched to Newgate prison.10
It seems inevitable that the power claimed by Parliament would have been abused. Unquestionably it was. A few examples illustrate the way in which individual rights were infringed. During the seventeenth century, there was a violent upheaval, both religious and political. This was the time of the Reformation and the establishment of the Church of England. It was also the period when the Stuarts proclaimed that the royal prerogative was absolute. Ultimately there were two revolutions, one protracted and bloody, the second without bloodshed. Critical commentary of all kinds was treated as contempt of Parliament in these troubled days. Even clergymen were imprisoned for remarks made in their sermons.11 Perhaps the outstanding case arose from the private conversation of one Floyd, a Catholic, in which he expressed pleasure over the misfortune of the King’s Protestant son-in-law and his wife. Floyd was not a member of Parliament. None of the persons concerned was in any way connected with the House of Commons. Nevertheless, that body imposed an humiliating and cruel sentence upon Floyd for contempt.12 The House of Lords intervened, rebuking the Commons for their extension of the privilege. The Commons acceded and transferred the record of the case to the Lords, who imposed substantially the same penalty.13
Later in that century, during the reign of Charles II, there was great unrest over the fact that the heir apparent, James, had embraced Catholicism. Anti-Catholic feeling ran high, spilling over a few years later when the infamous rogue, Titus Oates, inflamed the country with rumors of a “Popish Plot” to murder the King. A committee of Parliament was appointed to learn the sources of certain pamphlets that had
*235been appearing. One was entitled: The Grand Question Concerning the Prorogation of this Parliament for a Year and Three Months Stated and Discussed. A Doctor Carey admitted to the committee that he knew the author, but refused to divulge his name. Brought to the bar of the House of Lords, he persisted in this stand. The House imposed a fine of £1,000 and committed the witness to the Tower.14
A hundred years later, George III had managed to gain control of Parliament through his ministers. The King could not silence the opposition, however, and one of the most vocal was John Wilkes. This precipitated a struggle that lasted for several years until Wilkes finally prevailed. One writer sums up the case thus:
“He had won a victory for freedom of the press. He had directed popular attention to the royally-controlled House of Commons, and pointed out its unrepresentative character, and had shown how easily a claim of privilege might be used to sanction the arbitrary proceedings of ministers and Parliament, even when a fundamental right of the subject was concerned. It is one of life’s little ironies that work of such magnitude had been reserved for one of the worst libertines and demagogues of all time.”15
Even as late as 1835, the House of Commons appointed a select committee to inquire into “. . . the origin, nature, extent and tendency of the Orange Institutions.” This was a political-religious organization, vehemently Protestant in religion and strongly in favor of the growth of the Eritish Empire. The committee summoned the Deputy Grand Secretary and demanded that he produce all the records of the organization. The witness refused to turn over a letter-book, which he admitted contained his answers to many communications upon Orange business. But it also contained, he said, records of private communications with respect to Orangeism. Summoned to the bar of the House of Commons, he remained adamant and was committed to Newgate prison.16
Modern times have seen a remarkable restraint in the use by Parliament of its contempt power. Important investigations, like those conducted in America by congressional committees, are made by Royal Commissions of Inquiry.17 These commissions are comprised of experts in the problem to be studied. They are removal from the turbu-' lent forces of politics and partisan considerations. Seldom, if ever, have these commissioins been given the authority to compel the testimony of witnesses or the production of documents.18 Their success in ful*236filling their fact-finding missions without resort to coercive tactics is a tribute to the fairness of the processes to the witnesses and their close adherence to the subject matter committed to them.
The history of contempt of the legislature in this country is notably different from that of England. In the early days of the United States, there lingered the direct knowledge of the evil effects of absolute power. Most of the instances of use of compulsory process by the first Congresses concerned matters affecting the qualification or integrity of their members or came about in inquiries dealing with suspected corruption or mismanagement of government officials.19 Unlike the English practice, from the very outset the use of contempt power by the legislature was deemed subject to judicial review.20
There was very little use of the power of compulsory process in early years to enable the Congress to obtain facts pertinent to the enactment of new statutes or the administration of existing laws. The first occasion for such an investigation arose in 1827 when the House of Representatives was considering a revision of the tariff laws.21 In the Senate, there was no use of a fact-finding investigation in aid of legislation until 1859.22 In the Legislative Reorganization Act, the Committee on Un-American Activities is the only standing committee of the House of Representatives that was given the power to compel disclosures.23
It is not surprising, from the fact that the Houses of Congress so *237sparingly employed the power to conduct investigations, that there have been few cases requiring judicial review of the power. The nation was almost one hundred years old before the first case reached this Court to challenge the use of compulsory process as a legislative device, rather than in inquiries concerning the elections or privileges of Congressmen.24 In Kilbourn v. Thompson, 103 U. S. 168, decided in 1881, an investigation had been authorized by the House of Representatives to learn the circumstances surrounding the bankruptcy of Jay Cooke & Company, in which the United States had deposited funds. The committee became particularly interested in a private real estate pool that was a part of the financial structure. The Court found that the subject matter of the inquiry was “in its nature clearly judicial and therefore one in respect to which no valid legislation could be enacted.” The House had thereby exceeded the limits of its own authority.
Subsequent to the decision in Kilbourn, until recent times, there were very few cases dealing with the investigative power.25 The matter came to the fore again when the Senate undertook to study the corruption in handling of oil leases in the 1920’s. In McGrain' v. Daugherty, 273 U. S. 135, and Sinclair v. United States, 279 U. S. 263, the Court applied the precepts of Kilbourn to uphold the authority of the Congress to conduct the challenged investigations. The Court recognized the danger to effective and honest conduct of the Government if the legislature’s power to probe corruption in the executive branch were unduly hampered.
Following these important decisions, there was another lull in judicial review of investigations. The absence of challenge, however, was not indicative of the absence of inquiries. To the contrary, there was vigorous use of the investigative process by a Congress bent upon harnessing and directing the vast economic and social forces of the times. Only one case came before this Court, and the authority of the Congress was affirmed.26
*238In the decade following World War II, there appeared a new kind of congressional inquiry unknown in prior periods of American history. Principally this was the result of the various investigations into the threat of subversion of the United States Government, but other subjects of congressional interest also contributed to the changed scene. This new phase of legislative inquiry involved a broad-scale intrusion into the lives and affairs of private citizens. It brought before the courts novel questions of the appropriate limits of congressional inquiry. Prior cases, like Kilbourn, McGrain and Sinclair, had defined the scope of investigative power in terms of the inherent limitations of the sources of that power. In the more recent cases, the emphasis shifted to problems of accommodating the interest of the Government with the rights and privileges of individuals. The central theme was the application of the Bill of Rights as a restraint upon the assertion of governmental power in this form.
It was during this period that the Fifth Amendment privilege against self-incrimination was frequently invoked and recognized as a legal limit upon the authority of a committee to require that a witness answer its questions.27 Some early doubts as to the applicability of that privilege before a legislative committee never matured.28 When the matter reached this Court, the Government did not challenge in any way that the Fifth Amendment protection was available to the witness, and such a challenge could not have prevailed. It confined its argument to the character of the answers sought and to the adequacy of the claim of privilege. Quinn v. United States, 349 U. S. 155; Emspak v. United States, 349 U. S. 190; Bart v. United States, 349 U. S. 219.29
*239A far more difficult task evolved from the claim by witnesses that the committees’ interrogations were infringements upon the freedoms of the first Amendment.30 Clearly, an investigation is subject to the command that the Congress shall make no law abridging freedom of speech or press or assembly. While it is true that there is no statute to be reviewed, and that an investigation is not a law, nevertheless an investigation is part of law-making. It is justified solely as an adjunct to the legislative process. The First Amendment may be invoked against infringement of the protected freedoms by law or by law-making.31
Abuses of the investigative process may imperceptibly lead to abridgment of protected freedoms. The mere summoning of a witness and compelling him to testify, against his will, about his beliefs, expressions or associations is a measure of governmental interference. And when those forced revelations concern matters that are unorthodox, unpopular, or even hateful to the general public, the reaction in the life of the witness may be disastrous. This effect is even more harsh when it is past beliefs, expressions or associations that are disclosed and judged by current standards rather than those contemporary with the matters exposed. Nor does the witness alone suffer the consequences. Those who are identified by witnesses and thereby placed in the same glare of publicity are equally subject to public stigma, scorn and obloquy. Beyond that, there is the more subtle and immeasurable effect upon those who tend to adhere to the most orthodox and uncontroversial views and associations in order to avoid a similar fate at some future time. That this impact is partly the result of non-governmental activity by private persons cannot relieve the investigators of their responsibility for initiating the reaction.
The Court recognized the restraints of the Bill of Rights upon congressional investigations in United States v. Rumely, 345 U. S. 41. The magnitude and complexity of the problem of applying the First Amendment to that case led the Court to construe narrowly the resolution describing the committee’s authority. It was concluded that, when First Amendment rights are threatened, the delegation of power to the committee must be clearly revealed in its charter.
*240Accommodation of the congressional need for particular information with the individual and personal interest in privacy is an arduous and delicate task for any court. We do not underestimate the difficulties that would attend such an undertaking. It is manifest that despite the adverse effects which follow upon compelled disclosure of private matters, not all such inquiries are barred. Kilbourn v. Thompson teaches that such an investigation into individual affairs is invalid if unrelated to any legislative purpose. That is beyond the powers conferred upon the Congress in the Constitution. United States v. Rumely makes it plain that the mere semblance of legislative purpose would not justify an inquiry in the face of the Bill of Rights. The critical element is the existence of, and the weight to be ascribed to, the interest of the Congress in demanding disclosures from an unwilling witness. We cannot simply assume, however, that every congressional investigation is justified by a public need that overbalances any private rights affected. To do so would be to abdicate the responsibility placed by the Constitution upon the judiciary to insure that the Congress does not unjustifiably encroach upon an individual’s right to privacy nor abridge his liberty of speech, press, religion or assembly.
Petitioner has earnestly suggested that the difficult questions of protecting these rights from infringement by legislative inquiries can be surmounted in this case because there was no public purpose served in his interrogation. His conclusion is based upon the thesis that the Subcommittee was engaged in a program of exposure for the sake of exposure. The sole purpose of the inquiry, he contends, was to bring down upon himself and others the violence of public reaction because of their past beliefs, expressions and associations. In support of this argument, petitionef has marshalled an impressive array of evidence that some Congressmen have believed that such was their duty, or part of it.32
*241We have no doubt that there is no congressional power to expose for the sake of exposure. The public is, of course, entitled to be informed concerning the workings of its government.33 That cannot be inflated into a general power to expose where the predominant result can only be an invasion of the private rights of individuals. But a solution to our problem is not to be found in testing the motives of committee members for this purpose. Such is not our function. Their motives alone would not vitiate an investigation which had been instituted by a House of Congress if that assembly’s legislative purpose is being served.34
Petitioner’s contentions do point to a situation of particular significance from the standpoint of the constitutional limitations upon congressional investigations. The theory of a committee inquiry is that the committee members are serving as the representatives of the parent assembly in collecting information for a legislative purpose. Their function is to act as the eyes and ears of the Congress in obtaining facts upon which the full legislature can act. To carry out this mission, committees and subcommittees, sometimes one Congressman, are endowed with the full power of the Congress to compel testimony. In this case, only two men exercised that authority in demanding information over petitioner’s protest.
An essential premise in this situation is that the House or Senate shall have instructed the committee members on what they are to do with the power delegated to them. It is the responsibility of the Congress, in the first instance, to insure that compulsory process is used only in furtherance of a legislative purpose. That requires that the instructions to an investigating committee spell out that group’s jurisdiction and purpose with sufficient particularity. Those instructions are embodied in the authorizing resolution. That document is the committee’s charter. Broadly drafted and loosely worded, however, such resolutions can leave tremendous latitude to the discretion of the investigators. The more vague the committee’s charter is, the greater becomes the possibility that *242the committee’s specific actions are not in conformity with the will of the parent House of Congress.
The authorizing resolution of the Un-American Activities Committee was adopted in 1938 when a select committee, under the chairmanship of Representative Dies, was created.35 Several years later, the Committee was made a standing organ of the House with the same mandate.36 It defines the Committee’s authority as follows:
“The Committee on Un-American Activities, as a whole or by subcommittee, is authorized to make from time to time investigations of (i) the extent, character, and objects of un-American propaganda activities in the United States, (ii) the diffusion within the United States of subversive and un-American propaganda that is instigated from foreign countries or of a domestic origin and attacks the principle of the form of government as guaranteed by our Constitution, and (iii) all other questions in relation thereto that would aid Congress in any necessary remedial legislation.”37
It would be difficult to imagine a less explicit authorizing resolution. Who can define the meaning of “un-American”? What is that single, solitary “principle of the form of government as guaranteed by our Constitution”?38 There is no need to dwell upon the language, however. At one time, perhaps, the resolution might have been read narrowly to confine the Committe to the subject of propaganda.39” The events that have transpired in the fifteen years before the interrogation of petitioner make such a construction impossible at this date.
The members of the Committee have clearly demonstrated that they did not feel themselves restricted in any way to propaganda in the narrow sense of the word.40 Unquestionably the Committee conceived of its task *243in the grand view of its name. Un-American activities were its target, no matter how or where manifested. Notwithstanding the broad purview of the Committee’s experience, the House of Representatives repeatedly approved its continuation. Five times it extended the life of the special committee.41 Then it made the group a standing committee of the House.42 A year later, the Committee’s charter was embodied in the Legislative Reorganization Act.43 On five occasions, at the beginning of sessions of Congress, it has made the authorizing resolution part of the rules of the House.44 On innumerable occasions, it has passed appropriation bills to allow the Committee to continue its efforts.
Combining the language of the resolution with the construction it has been given, it is evident that the preliminary control of the Committee exercised by the House of Representatives is slight or nonexistent. No one could reasonably deduce from the charter the kind of investigation that the Committee was directed to make. As a result, we are asked to engage in a process of retroactive rationalization. Looking backward from the events that transpired, we are asked to uphold the Committee’s actions unless it appears that they were clearly not authorized by the charter. As a corollary to this inverse approach, the Government urges that we must view the matter hospitably to the power of the Congress — that if there is any legislative purpose which might have been furthered by the kind of disclosure sought, the witness must be punished for withholding it. No doubt every reasonable indulgence of legality must be accorded to the actions of a coordinate branch of our Government. But such deference cannot yield to an unnecessary and unreasonable dissipation of precious constitutional freedoms.
The Government contends that the public interest at the core of the investigations of the Un-American Activities Committee is the need by the Congress to be informed of efforts to overthrow the Government by force and violence so that adequate legislative safeguards can be erected. From this core, however, the Committee can radiate outward infinitely to any topic thought to be related in some way to armed insurrection. The outer reaches of this domain are known only by the content of “un-American activities.” Remoteness of subject can be aggravated by a probe for a depth of detail even farther removed from any basis of legislative action. A third dimension is added when the invest-*244gators turn their attention to the past to collect minutiae on remote topics, on the hypothesis that the past may reflect upon the present.
The consequences that flow from this situation are manifold. In the first place, a reviewing court is unable to make the kind of judgment made by the Court in United States v. Rumely, supra. The Committee is allowed, in essence, to define its own authority, to choose the direction and focus of its activities. In deciding what to do with the power that has been conferred upon them, members of the Committee may act pursuant to motives that seem to them to be the highest. Their decisions, nevertheless, can lead to ruthless exposure of private lives in order to gather data that is neither desired by the Congress nor useful to it. Yet it is impossible in this circumstance, with constitutional freedoms in jeopardy, to declare that the Committee has ranged beyond the area committed to it by its parent assembly because the boundaries are so nebulous.
More important and more fundamental than that, however, it insulates the House that has authorized the investigation from the witnesses who are subjected to the sanctions of compulsory process. There is a wide gulf between the responsibility for the use of investigative power and the actual exercise of that power. This is an especially vital consideration in assuring respect for constitutional liberties. Protected freedoms should not be placed in danger in the absence of a clear determination by the House or the Senate that a particular inquiry is justified by a specific legislative need.
It is, of course, not the function of this Court to prescribe rigid rules for the Congress to follow in drafting resolutions establishing investigating committees. That is a matter peculiarly within the realm of the legislature, and its decisions will be accepted by the courts up to the point where their own duty to enforce the constitutionally protected rights of individuals is affected. An excessively broad charter, like that of the House Un-American Activities Committee, places the courts in an untenable position if they are to strike a balance between the public need for a particular interrogation and the right of citizens to carry on their affairs free from unnecessary governmental interference. It is impossible in such a situation to ascertain whether any legislative purpose justifies the disclosures sought and, if so, the importance of that information to the Congress in furtherance of its legislative function. The reason no court can make this critical judgment is that the House of Representatives itself has never made it. Only the legislative assembly initiating an investigation can assay the relative necessity of specific disclosures.
Absence of the qualitative consideration of petitioner’s questioning by the House of Representatives aggravates a serious problem, revealed in this case, in the relationship of congressional investigating committees and the witnesses who appear before them. Plainly these committees are restricted to the missions delegated to them, i. e., to acquire certain data to be used by the House or the Senate in coping with a problem that falls within its legislative sphere. No witness can be compelled to make disclosures on matters outside that area. This is a jurisdictional *245concept of pertinency drawn from the nature of a congressional committee’s source of authority. It is not wholly different from nor unrelated to the element of pertinency embodied in the criminal statute under which petitioner was prosecuted. When the definition of jurisdictional pertinency is as uncertain and wavering as in the case of the Un-American Activities Committee, it becomes extremely difficult for the Committee to limit its inquiries to statutory pertinency.
Since World War II, the Congress has practically abandoned its original practice of utilizing the coercive sanction of contempt proceedings at the bar of the House. The sanction there imposed is imprisonment by the House until the recalcitrant witness agrees to testify or disclose the matters sought, provided that the incarceration does not extend beyond adjournment. The Congress has instead invoked the aid of the federal judicial system in protecting itself against contumacious conduct. It has become customary to refer these matters to the United States Attorneys for prosecution under criminal law.
The appropriate statute is found in 2 U. S. C. §192. It provides:
“Every person who having been summoned as a witness by the authority of either House of Congress to give testimony or to produce papers upon any matter under inquiry before either House, or any joint committee established by a joint or concurrent resolution of the two Houses of Congress, or any committee of either House of Congress, willfully makes default, or who, having appeared, refuses to answer any question pertinent to the question under inquiry, shall be deemed guilty of a misdemeanor, punishable by a fine of not more than $1,000 nor less than $100 and imprisonment in a common jail for not less than one month nor more than twelve months.”45
In fulfillment of their obligation under this statute, the courts must accord to the defendants every right which is guaranteed to defendants in all other criminal.cases. Among these is the right to have available, through a sufficiently precise statute, information revealing the stand*246ard of criminality before the commission of the alleged offense.46 Applied to persons prosecuted under §192, this raises a special problem in that the statute defines the crime as refusal to answer “any question pertinent to the question under inquiry.” Part of the standard of criminality, therefore, is the pertinency of the questions propounded to the witness.47
The problem attains proportion when viewed from the standpoint of the witness who appears before a congressional committee. He must decide at the time the questions are propounded whether or not to answer. As the Court said in Sinclair v. United States, 279 U. S. 263, the witness acts at his peril. He is “. . . bound rightly to construe the statute.” Id., at 299. An erroneous determination on his part, even if made in the utmost good faith, does not exculpate him if the court should later rule that the questions were pertinent to the question under inquiry.
It is obvious that a person compelled to make this choice is entitled to have knowledge of the subject to which the interrogation is deemed pertinent. That knowledge must be available with the same degree of explicitness and clarity that the Due Process Clause requires in the expression of any element of a criminal offense. The “vice of vagueness”48 must be avoided here as in all other crimes. There are several sources that can outline the “question under inquiry” in such a way that the rules against vagueness are satified. The authorizing resolution, the remarks of the chairman or members of the committee, or even the nature of the proceedings themselves might sometimes make the topic clear. This case demonstrates, however, that these sources often leave the matter in grave doubt.
The first possibility is that the authorizing resolution itself will so clearly declare the “question under inquiry” that a witness can understand the pertinency of questions asked him. The Government does not contend that the authorizing resolution of the Un-American Activities Committee could serve such a purpose. Its confusing breadth is amply illustrated by the innumerable and diverse questions into which the Committee has inquired under this charter since 1938. If the “question under inquiry” were stated with such sweeping and uncertain scope, we doubt that it would withstand an attack on the ground of vagueness.
That issue is not before us, however, in light of the Government’s position that the immediate subject under inquiry before the Subcommittee interviewing petitioner was only one aspect of the Committee’s authority to investigate un-American activities. Distilling that single topic from the broad field is an extremely difficult task upon the record before us. There was an opening statement by the Committee Chairman at the outset of the hearing, but this gives us no guidance. In this *247statement, the Chairman did no more than paraphrase the authorizing resolution and give a very general sketch of the past efforts of the Committee.49
No aid is given as to the “question under inquiry” in the action of the full Committee that authorized the creation of the Subcommittee before which petitioner appeared. The Committee adopted a formal resolution giving the Chairman the power to appoint subcommittees “. . . for the purpose of performing any and all acts which the Com*248mittee as a whole is authorized to do.”50 In effect, this was a device to enable the investigations to proceed with a quorum of one or two members and sheds no light on the relevancy of the questions asked of petitioner.51
The Government believes that the topic of inquiry before the Subcommittee concerned Communist infiltration in labor. In his introductory remarks, the Chairman made reference to a bill, then pending before the Committee,52 which would have penalized labor unions controlled or *249dominated by persons who were, or had been, members of a “Communist-action” organization, as defined in the Internal Security Act of 1950. The Subcommittee, it is contended, might have been endeavoring to determine the extent of such a problem.
This view is corroborated somewhat by the witnesses who preceded and followed petitioner before the Subcommittee. Looking at the entire hearings, however, there is strong reason to doubt that the subject revolved about labor matters. The published transcript is entitled: Investigation of Communist Activities in the Chicago Area, and six of the nine witnesses had no connection with labor at all.”53
The most serious doubts as to the Subcommittee’s “question under inquiry,” however, stem from the precise questions that petitioner has been charged with refusing to answer. Under the terms of the statute, after all, it is these which must be proved pertinent. Petitioner is charged with refusing to tell the Subcommittee whether or not he knew that certain named persons had been members of the Communist Party in the past. The Subcommittee’s counsel read the list from the testimony of a previous witness who had identified them as Communists. Although this former witness was identified with labor, he had not stated that the persons he named were involved in union affairs. Of the thirty names propounded to petitioner, seven were completely unconnected with organized labor. One operated a beauty parlor. Another was a watchmaker. Several were identified as “just citizens” or “only Communists.” When almost a quarter of the persons on the list are not labor people, the inference becomes strong that the subject before the Subcommittee was not defined in terms of Communism in labor.
The final source of evidence as to the “question under inquiry” is the Chairman’s response when petitioner objected to the questions on the grounds of lack of pertinency. The Chairman then announced that the Subcommittee was investigating “subversion and subversive propaganda.”54 This is a subject at least as broad and indefinite as the authorizing resolution of the Committee, if not more so.
*250Having exhausted the several possible indicia of the “question under inquiry,” we remain unenlightened as to the subject to which the questions asxed petitioner were pertinent. Certainly, if the point is that o„sour a alter trial and appeal, it was not adequately revealed to petitioner when he had to decide at his peril whether or not to answer. Fundamental fairness demands that no witness be compelled to make such a determination with so little guidance. Unless the subject matter lias been made io appear with undisputable clarity, it is the duty of the investiga rive body, upon objection of the witness on grounds of per-tinency, to slate for the record the subject under inquiry at that time and the manner in which the propounded questions are pertinent thereto.-55 To be meaningful, the explanation must describe what the topic under inquiry is and the connective reasoning whereby the precise questions asked relate to it.
The statement of the Committee Chairman in this case, in response to petitioner’s protest, was woefully inadequate to convey sufficient information as to the pertinency of the questions to the subject under inquiry. Petitioner was thus not accorded a fair opportunity to determine whether he was within his rights in refusing to answer, and his conviction is necessarily invalid under the Due Process Clause of the Fifth Amendment.
We are mindful of the complexities of modern government and the ample scope that must be left to the Congress as the sole constitutional depository of legislative power. Equally mindful are we of the indispensable function, in the exercise of that power, of congressional investigations. The conclusions we have reached in this case will not prevent the Congress, through its committees, from obtaining any information it needs for the proper fulfillment of its role in our scheme of government. The legislature is free to determine the kinds of data that should be collected. It is only those investigations that are conducted by use of compulsory process that give rise to a need to protect the rights of individuals against illegal encroachment. That protection can be readily achieved through procedures which prevent the separation of power from responsibility and which provide the constitutional requisites of fairness for witnesses. A measure of added care on the part of the House and the Senate in authorizing the use of compulsory process and by their committees in exercising that power would suffice. That is a small price to pay if it serves to uphold the principles of limited, constitutional government without constricting the power of the Congress to inform itself.
*251The judgment of the Court of Appeals is reversed, and the case is remanded to the District Court with instructions to dismiss the indictment.
It is so ordered.
MR. JUSTICE BURTON and MR. JUSTICE WHITTAKER took no part in the consideration or decision of this case.