On November 30, 1803 France formally transferred 828,000 square miles to the United States in exchange for USD 15 million. This land, the Louisiana Purchase, doubled the size of the nation. While negotiations for this deal had been going on, Thomas Jefferson had already begun thinking about a transcontinental expedition to explore the lands west of the Mississippi. Besides the commercial and scientific benefits of such an exploration, there was the issue of asserting America's sovereignty over the new territory. Meriwether Lewis and William Clark were hired to undertake this journey. The Corps of Discovery, as the group is often referred to, kept detailed journals on the flora and fauna they observed, and members of their team were also the first non-Indians to make contact with a number of tribes. Sacajawea, the Shoshone wife of French-Canadian trapper Toussaint Charbonneau, served as their guide and interpreter for much of the trip. Encyclopedia of the Lewis and Clark Expedition provides a complete reference on this great American expedition, covering all major elements of the expedition from the preparatory work initiated by President Thomas Jefferson in 1801 to the corps' return from the Pacific Ocean in 1806. Containing a wealth of informative A-to-Z entries, as well as a timeline, an introductory essay, supporting back-matter, and many maps and photos, this is a must-have reference that details a fascinating expedition that has played such an important role in American history.