A programmable cylinder lock includes a stator and a cylindrical rotor mounted therein, having a keyhole and including inside the rotor key followers movable along the longitudinal and transversal directions, and locking pins movable along the longitudinal direction, the followers and locking pins forming together a number of pairs and having toothings for mutually cooperating to define the lock codification, the rotor including a stop bar cooperating with a longitudinal groove of the stator and cooperating with the locking pins, and a change bar slidingly coupled with the followers to keep them engaged with the pins and disengage them therefrom when the bar provides a lock programming position. The bar has projections facing the keyhole, and the use key has corresponding recesses to face the projections when correctly inserted in the lock, whereas the change key has a longitudinal groove extending in a position corresponding to the use key recesses.