The Library of Congress of the United States is one of the most important libraries in the world. Originally founded as a research library for the United States Congress in 1815, its original collection were the books of former U.S. President Thomas Jefferson. Later the Library assumed a role as a legal repository to guarantee copyright protection. All authors seeking American copyright had to submit two copies of the work to the Library. This requirement is no longer enforced.
Main Library of Congress Building at the start of the 20th century
The Library also developed a system of book classification called Library of Congress classification (LC) which is used by most research and university libraries, although most public libraries continue to use the Dewey decimal system.
With over 115 million items, it is one of the largest libraries in the history of the world, surpassed only by the British Library, which contains over 150 million items.
The United States Library of Congress is a source for public domain image resources such as those used in the Wikipedia.
The library is open to the general public for academic research, and runs tours for visitors.