A camshaft assembly comprises an inner shaft 12 and an outer tube 14 surrounding and rotatable relative to the inner shaft. Two groups of cam lobes are mounted on the outer tube 14 , the first group of cam lobes 16 being fast in rotation with the outer tube 14 and the second group of lobes 26 being rotatably mounted on the outer surface of the tube 14 and connected for rotation with the inner shaft by means of pins 22 that pass with clearance through slots in the outer tube 14 . A sleeve 20 rotatably mounted on the outer tube 14 is connected to impart drive to the inner shaft 12 by means of a pin 24 passing with clearance through a circumferentially extending slot in the outer tube 14.