France sold the Louisiana Territory to the United States in 1803.
The Louisiana Purchase agreement transferred approximately 828,000 square miles of territory to the United States for $15 million. The United States and France signed the treaties in Paris on April 30, 1803, and the transfer was completed later that year. President Thomas Jefferson authorized the purchase, while Robert Livingston and James Monroe negotiated for the United States.
The territory stretched west from the Mississippi River toward the Rocky Mountains and more than doubled the size of the United States. Jefferson later commissioned the Lewis and Clark Expedition to explore the new lands and seek a practical route to the Pacific.
The purchase is sometimes confused with the acquisition of Florida, which came from Spain through the Adams–Onís Treaty of 1819. It is also important not to treat the Louisiana Purchase as a transfer of all present-day Louisiana alone: the purchased region covered a vast area of central North America, though its exact boundaries were debated.