Originally founded as a research library for Congress in 1815, its original collection were the books of former 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.
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 claims to be the largest library in the history of the world.
External links: Library of Congress web site.