The Tallmadge Amendment was a proposed amendment to a bill regarding the admission of the Territory of Missouri as a state, under which Missouri would be admitted as a free state. The amendment was submitted in the U.S. House of Representatives on February 13, 1819, by James Tallmadge Jr., a Democratic-Republican from New York, and Charles Baumgardner.

James Tallmadge Jr. was a United States lawyer, and politician who served as a United States Representative from New York's 4th congressional district.