Instances of book thefts in Europe and America from earliest times are cited with particular attention to the activities of the most famous of book thieves, Count Guglielmo Libri. Types of book thieves are described: the librarian, college instructor, graduate student, member of the cloth, reader, hobbyist, bookseller. Measures taken to secure against book thefts are discussed: work of the American Library Association's Security Committee; of AB Bookman's Weekly; Bookline Alert: Missing Books and Manuscripts (Bam-Bam); and the Antiquarian Booksellers Association of America's security program as outlined in John Jenkins' Rare Books and Manuscript Thefts: A Security System for Librarians, Booksellers, and Collectors. A concluding decalogue of injunctions is given, designed for the prevention of book thefts and the apprehension of book thieves.