The Thomas Jefferson Building, also known as the Main Library, is the oldest of the Library of Congress buildings in Washington, D.C. Built between 1890 and 1897, it was initially known as the Library of Congress Building. In 1980, the building was named in honor of Thomas Jefferson (1743–1826), a Founding Father, the principal author of the Declaration of Independence, and the third U.S. president. In 1815, the purchase of Jefferson's book collection formed a core foundation for the library's collection.
The building is located on First Street, S.E. between Independence Avenue and East Capitol Street in the federal national capital city of Washington, D.C., across from the United States Capitol on Capitol Hill. It is adjacent to the library's additional buildings in the Library of Congress complex, the John Adams Building (built in the 1930s) across Second Street, and the James Madison Memorial Building (built in the 1970s) across Independence Avenue to the south.