The Library of Congress is the de facto national library of the United States and the research arm of the United States Congress. 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. Its collections include more than 32 million catalogued books and other print materials in 470 languages; more than 61 million manuscripts; the largest rare book collection in North America, including the rough draft of the Declaration of Independence, a Gutenberg Bible (one of only four perfect vellum copies known to exist); over 1 million US government publications; 1 million issues of world newspapers spanning the past three centuries; 33,000 bound newspaper volumes; 500,000 microfilm reels; over 6,000 comic book titles; the world's largest collection of legal materials; films; 4.8 million maps; sheet music; 2.7 million sound recordings; more than 13.7 million Prints & Photographs images including fine and popular art pieces and architectural drawings; the Betts Stradivarius; and the Cassavetti Stradivarius. The head of the Library is the Librarian of Congress, currently James H. Billington.