The Louisiana Purchase (French: Vente de la Louisiane "Sale of Louisiana") is the acquisition of the Louisiana territory (828,000 square miles or 2.14 million km²) by the United States from France in 1803.

The U.S. pays fifty million francs ($11,250,000) and a cancellation of debts worth eighteen million francs ($3,750,000) for a total of sixty-eight million francs ($15 million, equivalent to $300 million in 2016).

The Louisiana territory includes land from fifteen present U.S. states and two Canadian provinces.

The territory contains land that forms Arkansas, Missouri, Iowa, Oklahoma, Kansas, and Nebraska; the portion of Minnesota west of the Mississippi River; a large portion of North Dakota; a large portion of South Dakota; the northeastern section of New Mexico; the northern portion of Texas; the area of Montana, Wyoming, and Colorado east of the Continental Divide; Louisiana west of the Mississippi River (plus New Orleans); and small portions of land within the present Canadian provinces of Alberta and Saskatchewan. Its non-native population was around sixty thousand inhabitants, of whom half are enslaved Africans.

The Kingdom of France had controlled the Louisiana territory from 1699 until it was ceded to Spain in 1762.

In 1800, Napoleon, then the First Consul of the French Republic, hoping to re-establish an empire in North America, had regained ownership of Louisiana.

However, France's failure to put down the revolt in Saint-Domingue, coupled with the prospect of renewed warfare with the United Kingdom, prompts Napoleon to sell Louisiana to the United States to fund his military.

The Americans originally sought to purchase only the port city of New Orleans and its adjacent coastal lands, but quickly accept  the bargain.

The Louisiana Purchase occurs during the term of the third President of the United States, Thomas Jefferson.

Before the purchase is finalized, the decision faces Federalist Party opposition; they argue that it is unconstitutional to acquire any territory.

Jefferson agrees hat the U.S. Constitution does not contain explicit provisions for acquiring territory, but he asserts that his constitutional power to negotiate treaties is sufficient.