The key-operated locks described and assessed are the warded, disc or wafer tumbler, pin tumber, and lever. Combination locks are also described and assessed. The descriptions and assessments of lock bodies encompass bolts (latch bolt and deadbolt), door lock types (mortise, rim-mounted, tubular, cylindrical lockset, and unit locks), cylinders, padlocks, and strikes. The discussion of attacks on locks and countermeasures addresses surreptitious attacks, which include illicit keys, the circumvention of the internal barriers of the lock, manipulation, and shimming; and forceful attacks on bolts and cylinders. The discussion of the role of locks in the systems approach to security notes that the effectiveness of a lock depends on the effectiveness of the entire system, such as the door, the door frame, and the structure of the wall into which the door fits. Descriptive drawings and subject index.