A gun lock (10) to enclose the trigger and trigger guard of a gun. The gun lock (10) includes co-operating housing halves (60 and 61) which encompass the trigger and trigger guard. Extending between the housing halves (60 and 61) is an Alan screw which is tensioned and access to the Alan screw (73) is prevented by means of a cylinder lock locatable in a passage in one of the housing halves. The gun lock (10) can only be released upon removal of the cylinder lock providing access to the head of the Alan screw (73).