Abstract: A reprogrammable lock assembly of the wafer tumbler type which includes a plurality of wafer-type tumblers and cooperating followers mounted in a cylindrical plug and housing. The tumblers are movable radially in the plug to project beyond the plug into restricted pockets in the housing to maintain the lock in a locked position. A driver and adapter disposed in the opposite axial end of the housing from the key hole. The driver and adapter prevent rotation for unlocking unless a key having the proper length is inserted. In addition, the key must have the proper configuration to draw all of the tumblers within the confines of the plug in order to rotate the plug for reprogramming or unlocking of the door. The lock assembly is operated with a reprogramming key and a use key. A reprogramming key is used to rotate the plug to a resetting position which allows the tumblers to separate from the followers.