Harry Miller Lydenberg (November 18, 1874 – April 16, 1960) was an American librarian, author and book conservationist. He is best known for his decades-long career as a librarian and eventual director for the New York Public Library, American liaison to the international library community, as well as one of the 100 most important library innovators of the 20th century. His written works describe his preferred library reference, collection and conservation practices, as well as his knowledge of the New York Public Library.