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 Washington, D.C., it is the largest by shelf space and one of the most important libraries in the world. Its collections include more than 30 million catalogued books and other print materials in 470 languages; more than 58 million manuscripts; the largest rare book collection in North America, including 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 books titles; the world's largest collection of legal materials; films; 4.8 million maps; sheet music; 2.7 million sound recordings; the Betts Stradivarius; and the Cassavetti Stradivarius. The head of the Library is the Librarian of Congress.