This book examines aviation security with a focus on the background and policy options for screening and securing air cargo. The air cargo system is a complex, multi-faceted network that handles a vast amount of freight, express packages and mail carried aboard passenger and all-cargo aircraft. The air cargo system is vulnerable to several security risks, including potential plots to place explosives aboard aircraft; illegal shipments of hazardous materials; criminal activities such as smuggling and theft and potential hijackings and sabotage by persons with access to aircraft. Several procedural and technology-based initiatives to enhance air cargo security and deter terrorist and criminal threats have been put in place or are under construction.