The invention relates to a tool mounting arrangement comprising a movable arm carrying a tool holder and a tool rack for holding one or more tools selectively and releasably engageable by the tool holder. in order to avoid the need to incorporate a seienoid or an actuating piston in the robot arm, an actuating means (30) is associated with the tool rack and is operable to cause interconnection and disengagement between the tool holder (16) and a tool (10) in the rack.