The Louisiana Purchase was signed on April 30, 1803, with the treaty formally signed on May 2, 1803. This agreement was between the United States and France, through which the U.S. purchased about 828,000 square miles of territory west of the Mississippi River for $15 million. The purchase effectively doubled the size of the United States at the time and included land that would become parts of 15 present U.S. states and two Canadian provinces. The U.S. Senate approved the treaty for ratification later that year on October 20, 1803.