The Territory of Louisiana or Louisiana Territory was an organized incorporated territory of the United States that existed from July 4, 1805, until June 4, 1812, when it was renamed the Missouri Territory. The territory was formed out of the District of Louisiana, which consisted of the portion of the Louisiana Purchase north of the 33rd parallel.

The Louisiana Purchase was the acquisition of the territory of Louisiana by the United States from the French First Republic in 1803. This consisted of most of the land in the Mississippi River's drainage basin west of the river. In return for fifteen million dollars, or approximately eighteen dollars per square mile, the United States nominally acquired a total of 828,000 sq mi in Middle America. However, France only controlled a small fraction of this area, most of which was inhabited by Native Americans; effectively, for the majority of the area, the United States bought the preemptive right to obtain Indian lands by treaty or by conquest, to the exclusion of other colonial powers.