The 108th United States Congress was a meeting of the legislative branch of the United States federal government, composed of the United States Senate and the United States House of Representatives from January 3, 2003, to January 3, 2005, during the third and fourth years of George W. Bush's presidency.

House members were elected in the 2002 general election on November 5, 2002. Senators were elected in three classes in the 1998 general election on November 3, 1998, 2000 general election on November 7, 2000, or 2002 general election on November 5, 2002. The apportionment of seats in the House of Representatives was based on the 2000 United States census.

This is the most recent Congress to have a Democratic senator from South Carolina, Fritz Hollings, who retired at the end of the Congress.

Both chambers had a Republican majority, with the Republicans slightly increasing their edge in the House, and regaining control of the Senate, after party control had switched back and forth during the 107th Congress due to various factors. With President Bush, this gave the Republicans an overall federal government trifecta.

The party summary for the Senate remained the same during the entire 108th Congress.

Due to resignations and special elections, Republicans lost a net of two seats to the Democrats. All seats were filled though special elections. (See Changes in membership, below.)

Senators are preceded by the class, In this Congress, Class 3 meant their term ended with this Congress, requiring reelection in 2004; Class 1 meant their term began in the last Congress, requiring reelection in 2006; and Class 2 meant their term began in this Congress, requiring reelection in 2008.

Representatives are preceded by the district number.