The California Statehood Act, officially An Act for the Admission of the State of California into the Union and also known as the California Admission Act, is the federal legislation that admitted California to the United States as the thirty-first state. Passed in 1850 by the 31st United States Congress, the law made California one of only a few states to become a state without first being an organized territory.

The 31st 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, 1849, to March 4, 1851, during the 16 months of the Zachary Taylor presidency and the first eight months of the administration of Millard Fillmore's. The apportionment of seats in this House of Representatives was based on the 1840 United States census. The Senate had a Democratic majority, while there was a Democratic plurality in the House.