Meriwether Lewis and William Clark were explorers. This collection contains the manuscript journals kept by Lewis and Clark on their travels to the source of the Missouri River and across the continent to the Pacific Ocean. There are interlineations throughout by Nicholas Biddle, who published his narrative "History of the Expedition of Captains Lewis and Clark" (1814).

Founded in 1743 by Benjamin Franklin, the American Philosophical Society was the first learned society in the United States. For over 250 years, the Society has played an important role in American cultural and intellectual life. Until the mid-nineteenth century, the Society fulfilled the role of a national academy of science, national library and museum, and even patent office. Early members of the Society included Thomas Jefferson, David Rittenhouse, Benjamin Rush, Stephen Peter Du Ponceau, George Washington, and many other figures prominent in American history. The Archives of the American Philosophical Society consists of 192.25 linear feet of material, organized into thirteen record groups dating back to 1743. The Society's archives extensively documents not only the organization's historical development but also its role in American history and the history of science and technology.