Gun lock assembly

These and other objects are accomplished by a gun lock assembly having an engagement portion with a locked position in which a portion of the firing mechanism is operatively engaged to prevent firing of the firearm, and an unlocked position in which operation of the firearm is permitted. The lock preferably comprises a lock housing with structure for attaching the lock housing to the firearm. A combination lock is preferably provided with structure for altering the combination. A mounting plate for the lock is also described. Alternative lock constructions suitable with different types of firearms are also disclosed.