Types of Hearings
Committees hold legislative hearings on measures or policy issues that may become public law. Sometimes a committee holds hearings on multiple measures before ultimately choosing one vehicle for further committee and chamber action. Hearings provide a forum where facts and opinions can be presented from witnesses with varied backgrounds, including Members of Congress and other government officials, interest groups, and academics, as well as citizens likely to be directly or indirectly affected by the proposal.

Legislative hearings
Oversight hearings review or study a law, issue, or an activity, often focusing on the quality of federal programs and the performance of government officials. Hearings also help ensure that the execution of laws by the executive branch complies with legislative intent, and that administrative policies reflect the public interest. Oversight hearings often seek to improve the efficiency, economy, and effectiveness of government operations. A significant part of a committee's hearings workload is dedicated to oversight. For example, on a single day, May 8, 1996, the Senate Committee on Energy and Natural Resources held an oversight hearing to look into a recent increase in gasoline prices; the Committee on Governmental Affairs held an oversight hearing on the Internal Revenue Service; the Committee on Health, Education, Labor and Pensions held an oversight hearing on the implementation of the Family and Medical Leave Act; and the Committee on Indian Affairs held an oversight hearing on the impact of a recent Supreme Court case involving Indian gaming. Many committees oversee existing programs in the context of hearings on related legislation, or routinely perform oversight when it is time to reauthorize a program, so oversight hearings may be combined with legislative hearings.

Oversight hearings
Investigative hearings share some of the characteristics of legislative and oversight hearings. The difference lies in Congress's stated determination to investigate, usually when there is a suspicion of wrongdoing on the part of public officials acting in their official capacity, or private citizens whose activities suggest the need for a legislative remedy. Congress's authority to investigate is broad and it has exercised this authority since the earliest days of the republic. Its most famous inquiries are benchmarks in American history: Credit Mobilier, Teapot Dome, Army-McCarthy, Watergate, and Iran-Contra. Investigative hearings often lead to legislation to address the problems uncovered. Judicial activities in the same area of Congress's investigation may precede, run simultaneously with, or follow such inquiries.

Investigative hearings
Confirmation hearings on presidential nominations are held in fulfillment of the Senate's constitutional "advise and consent" responsibilities. Each Senate committee holds confirmation hearings on presidential nominations to executive and judicial positions within its jurisdiction. These hearings often offer an opportunity for oversight into the activities of the nominee's department or agency. While the vast majority of confirmation hearings are routine, some are controversial. Similarly, the Senate, as required by the Constitution, must consent to the ratification of treaties negotiated by the executive branch with foreign governments. In October 1999, for example, the Committee on Foreign Relations and the Committee on Armed Services held hearings on the Comprehensive Nuclear Test Ban Treaty. Also that year the Committee on Foreign Relations held hearings on ratifying tax treaties with Estonia, Venezuela, Denmark, and other nations. Although not as numerous as confirmation hearings, these hearings also allow the Senate to meet its constitutional responsibilities in an important area of public policy.

Confirmation hearings
Field hearings are Congressional hearings held outside Washington. The formal authority for field hearings is found implicitly in the chamber rules. Senate Rule XXVI, paragraph 1 states that a committee "is authorized to hold hearings … at such times and places during the sessions, recesses, and adjourned periods of the Senate" as it sees fit. Otherwise, there is no distinction between field hearings and those held in Washington. In the 106th Congress, for example, the Committee on Commerce has held a field hearing in Bellingham, Washington, on a liquid pipeline explosion in that city, and the Committee on Energy and Natural Resources has held a field hearing in Albuquerque, New Mexico, on a bill to review the ability of the National Laboratories to meet Department of Energy standards. While field hearings involve some matters different from Washington hearings, most of the procedural requirements are the same. However, funding for committee travel must meet regulations established by the Senate Committee on Rules and Administration.

Subpoenas and Depositions
The vast majority of committee hearings are open to the public, as required under Senate rules. But a hearing, like other committee meetings, may be closed for specific reasons stated in Senate rules (Rule XXVI, paragraph 5(b)). A committee may close a hearing if it (1) involves national security information; (2) concerns committee personnel, management, or procedures; (3) invades the personal privacy of an individual, damages an individual's reputation or professional standing, or chargebecas an individual with a crime or misconduct; (4) reveals identities or damage operations relating to law enforcement activities; (5) discloses certain kinds of confidential financial or commercial information; or (6) divulges information that other laws or regulations require to be kept confidential. The Senate rules also contain a specific procedure for closing a hearing. By motion of any Senator, if seconded, a committee may close a session temporarily to discuss whether there is a need to close a hearing for any of the reasons stated above. If so, the committee can close the hearing by majority roll call vote in open session. By this procedure, a committee can close a hearing or a series of sessions on a particular subject for no more than 14 calendar days.