For its first century and more, Congress depended largely on executive departments for facts and figures. As the federal government grew, Congress built its own sources of expertise: a reference service in 1914, an auditor in 1921, and a budget office in 1974, after clashes with the Nixon administration over spending. Today the legislative branch includes about a dozen agencies with thousands of employees.
This guide describes each major support agency, what it does, and how it shapes the work of Congress.
The Architect of the Capitol maintains the Capitol, the House and Senate office buildings, the Library of Congress buildings, and the U.S. Botanic Garden. The Capitol Police, established in 1828, protect members and the complex, under a board that includes both chambers' sergeants at arms. The Office of Congressional Workplace Rights enforces workplace laws for congressional employees, and the Office of Congressional Ethics reviews allegations against House members.
Congress also uses advisory commissions, such as the Medicare Payment Advisory Commission, to analyze complex programs. The Office of Technology Assessment advised Congress on science and technology from 1972 until it was defunded in 1995 as part of a push to shrink the legislative branch. Supporters of more support capacity argue Congress needs expertise to keep pace with the executive and with technology, while others say existing agencies are sufficient and question their accuracy or neutrality.
The Congressional Budget Office, created by the Congressional Budget and Impoundment Control Act of 1974, produces cost estimates for nearly every bill reported by a committee, along with long-term budget and economic projections. Its scores can make or break legislation, and lawmakers of both parties have both praised and criticized them. The Congressional Research Service, founded in 1914 as the Legislative Reference Service, answers tens of thousands of requests a year from members and staff and publishes reports that are now publicly available.
The Government Accountability Office, created in 1921 as the General Accounting Office and renamed in 2004, audits federal agencies, investigates waste and fraud, and issues legal decisions on how appropriations may be used, including whether agencies have violated the Antideficiency Act or the Impoundment Control Act. It is led by the Comptroller General, appointed to a 15-year term. GAO issued several decisions in 2025 finding that withholding of appropriated funds violated the Impoundment Control Act, findings the administration disputed.
The Library of Congress, founded in 1800, is the largest library in the world and includes the Copyright Office and CRS. Its leader, the Librarian of Congress, is appointed by the President with Senate confirmation, and the President's removal of the Librarian in 2025 raised disputes over whether the library functions as a legislative or executive agency. The Government Publishing Office, dating to 1861, produces official publications, including the Congressional Record and the Federal Register.
Independent sources of information let Congress check the executive branch on its own terms. Each support agency is funded through the annual legislative branch appropriations bill and answers to Congress rather than the President. Alongside personal and committee staff, these agencies form the institutional memory and analytical backbone of the legislative branch.
See the institution they serve in how Congress works, see their work in budget fights in how the federal budget works, or meet other watchdogs in federal watchdogs.