Major Stephen H. Long of the United States Army was the most important government-sponsored explorer in the decade after the War of 1812. He led three major and several minor expeditions up the Mississippi, Missouri, and Arkansas rivers and the Red River of the north, as well as exploring the central and southern Plains, the Front Range of the Rocky Mountains, and the Great Lakes. His companions included engineers, cartographers, naturalists, ethnologists,and artists, and they gathered a wealth of scientific, military, and artistic data about the interior of North America. For years Long's expeditions have been overlooked or misunderstood; here for the first time they are placed in the context of American scientific development.