"The Library of Congress is the research library of the United States Congress, de facto national library of the United States, and the oldest federal cultural institution in the United States. Located in three buildings in Washington, D.C., it is the largest library in the world by shelf space and holds the largest number of books.
The Library of Congress was established by Congress in 1800, and was housed in the Unites States Capitol for most of the 19th century. After much of the original collection had been destroyed during the War of 1812, Thomas Jefferson sold 6487 books, his entire personal collection, to the library in 1815. After a period of decline during the mid-19th century the Library of Congress began to grow rapidly in both size and importance after the American Civil War, culminating in the construction of a separate library building and the transference of all copyright deposit holdings to the Library. During the rapid expansion of the 20th century the Library of Congress assumed a preeminent public role, becoming a "library of last resort" and expanding its mission for the benefit of scholars and the American people.
The Library's primary mission is researching inquiries made by members of Congress through the Congressional Research Service; although it is open to the public, only legislators, Supreme Court justices and other high-ranking government officials may check out books. As the de facto national library, the Library of Congress promotes literacy and American literature through projects such as the American Folklife Center, American Memory, Center for the Book and Poet Laureate." - in: wikipedia