The 40th United States Congress was a meeting of the legislative branch of the United States federal government, consisting of the United States Senate and the United States House of Representatives. It met in Washington, D.C. from March 4, 1867, to March 4, 1869, during the third and fourth years of Andrew Johnson's presidency. The apportionment of seats in the House of Representatives was based on the 1860 United States census. Both chambers had a Republican majority. In the Senate, the Republicans had the largest majority a party has ever held.

The 39th United States Congress was a meeting of the legislative branch of the United States federal government, consisting of the United States Senate and the United States House of Representatives. It met in Washington, D.C., from March 4, 1865, to March 4, 1867, during Abraham Lincoln's final month as president, and the first two years of the administration of his successor, Andrew Johnson.