The Congressional Subway in Washington, D.C. is two underground electric subway systems that connect the U.S. Capitol building to the House and Senate office buildings. On the House side, an older human-controlled system with single, open-topped cars shuttles between the Rayburn House Office Building and the Capitol. On the Senate side, two separate subway systems exist. One is a computer-controlled system with small groups of enclosed cars that shuttle passengers between the Hart Senate Office Building, Dirksen Senate Office Building, and the Capitol. The second system is similar to the one found on the House side; it connects the Russell Senate Office Building and the Capitol. The House and Senate subway systems do not terminate in the same location under the Capitol, however they are connected by a labyrinth of underground tunnels.

The systems are open to members, their visitors, and individuals employed in the Capitol, House, and Senate office buildings, free of charge. The House system has human operators to provide patronage jobs and so that the operators can enforce the "members only" rules that limit nonmembers to certain sections of the cars or that prohibit them altogether during roll call votes.

The system was originally built in 1909 to link the Russell Senate Office Building to the Capitol. The Dirksen Senate Office Building was added to the system in 1954 and the Rayburn House Office Building in 1965. The system first ran on March 7, 1909, and was last updated in 1994.

See also United States Congress, US Capitol, Washington Metro.