The 18th 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, 1823, to March 4, 1825, during the seventh and eighth years of James Monroe's presidency. The apportionment of seats in the House of Representatives was based on the 1820 United States census. Both chambers had a Democratic-Republican majority.

The Federalist Party was a conservative and nationalist American political party and the first political party in the United States. It dominated the national government under Alexander Hamilton from 1789 to 1801. The party was defeated by the Democratic-Republican Party in 1800, and it became a minority party while keeping its stronghold in New England. It made a brief resurgence by opposing the War of 1812, then collapsed with its last presidential candidate in 1816. Remnants lasted for a few years afterwards.