Theft of books, especially rare books, is difficult to tally because of the reluctance of libraries to report losses. Large-scale losses, especially those perpetrated by insiders, occur with regularity. Outsider theft does occur, committed by knowledgeable thieves with expertise in penetrating library defenses. Prevention methods require application of the highest standards of security, including sophisticated electronics, tight key control, and supervised access screening. Package inspections, both incoming and outgoing, are standard procedures. This chapter defines the methods recommended for protecting these special collections and discusses the enforcement of screening procedures.