The libraries hold a collection of nearly 12 million items, 260,000 rare or special books, 3 million e-books, 1.5 million audiovisual materials, 75,000 serials, 6 million microform holdings, and thousands of other digital resources, making it one of the largest and most diverse academic library systems in the world.[12] Starting in 2004 the Stanford libraries have collaborated with Google in digitizing hundreds of thousands of books from the Stanford collections and making them available to readers worldwide at no charge.[13][14]