Kentucky and Virginia Resolutions, a series of resolutions denouncing the Alien and Sedition Acts of 1798. They were adopted by the legislatures of Kentucky (1798 and 1799) and Virginia (1798), and were the first important statements of the states' rights theory. Both legislatures claimed that the federal government had assumed powers belonging to the states, and that state governments had the right to decide whether an act of Congress was constitutional. The Kentucky resolutions of 1799 further asserted that the states could jointly nullify federal laws they considered unconstitutional.

Thomas Jefferson wrote the Kentucky resolutions of 1798 (anonymously, since he was Vice President). James Madison wrote the Virginia resolutions. The resolutions did not, however, win much support from other states.