A lock system for controlling access, for example to a room or building, is disclosed. The lock system comprises a bolt module in which control of the bolt can be configured differently on the two sides of a leaf or door. Control of the bolt module may be provided by various locking modules, which are also disclosed herein. The bolt module is reversible for left handed or right handed operation. In one embodiment the bolt module comprises: a bolt moveable between a thrown position and a retracted position; and a first rotor assembly capable of accepting a drive element, the first rotor assembly arranged to drive the bolt. The bolt module may also comprise a second rotor assembly. The bolt module may comprise an anti-thrust member obstructing driving back of the bolt under action of an external force on the bolt. The bolt module may comprise a lockable cover.