Abstract: A gun lock assembly includes 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 includes a lock housing with structure for attaching the lock housing to the firearm. An adapter can be utilized to facilitate attachment of the lock to a variety of different guns. A preferred combination lock is disclosed with structure for altering the combination. An embodiment that is suitable for long arms is also disclosed.