"Let the Land rejoice, for you have bought Louisiana for a Song."The Louisiana Purchase has been described as the greatest real estate deal in history. In 1803 the United States paid France $15 million for the Louisiana Territory--828,000 square miles of land west of the Mississippi River. The lands acquired stretched from the Mississippi River to the Rocky Mountains and from the Gulf of Mexico to the Canadian border. Thirteen states were carved from the Louisiana Territory. The Louisiana Purchase nearly doubled the size of the United States, making it one of the largest nations in the world.--Gen. Horatio Gates to President Thomas Jefferson, July 18, 1803
U.S. treaties with foreign powers are preserved at the National Archives.
Louisiana Purchase Treaty, April 30, 1803
The Louisiana Purchase consists of three separate agreements between the United States and France: a treaty of cession and two agreements providing for the exchange of monies in the transaction. The volume shown above is the French exchange copy of the convention providing for the settlement of an earlier debt owed by France to the United States. The first image shows the volume closed; the second shows the volume open to the page bearing Napoleon Bonaparte's signature.
You can read a textual transcription of the three agreements.
National Archives, General Records of the U.S. Government
National Archives and Records Administration