The Louisiana Purchase was the 1803 acquisition that nearly doubled the nominal size of the United States.
The United States purchased the Louisiana territory from France for $15 million. President Thomas Jefferson had initially sought control of New Orleans and the Mississippi River, which were vital to western farmers and trade. French Treasury Minister François Barbé-Marbois offered the entire territory, and American negotiators Robert Livingston and James Monroe accepted the opportunity. The agreement was signed in Paris on April 30, 1803, and the transfer was completed later that year.
The purchase covered a vast region west of the Mississippi River, although its exact boundaries were not fully understood at the time. It included land that later became part or all of fifteen present-day states and portions of two Canadian provinces. The acquisition is distinct from the later Alaska Purchase of 1867 and the Gadsden Purchase of 1853. Its scale made it one of the most consequential territorial changes in United States history.