The Library's mission is to make its resources available and useful to the Congress and the American people and to sustain and preserve a universal collection of knowledge and creativity for future generations.

Established with $5,000 appropriated by the legislation, the original library was housed in the new Capitol until August 1814, when invading British troops set fire to the Capitol Building, burning and pillaging the contents of the small library.

Within a month, retired President Thomas Jefferson offered his personal library as a replacement. Jefferson had spent 50 years accumulating books, "putting by everything which related to America, and indeed whatever was rare and valuable in every science"; his library was considered to be one of the finest in the United States. In offering his collection to Congress, Jefferson anticipated controversy over the nature of his collection, which included books in foreign languages and volumes of philosophy, science, literature, and other topics not normally viewed as part of a legislative library. He wrote, "I do not know that it contains any branch of science which Congress would wish to exclude from their collection; there is, in fact, no subject to which a Member of Congress may not have occasion to refer."