Abstract: A rotary internal combustion engine of the type having pistons mounted for reciprocatory movement in respective cylinders which are arranged in equally-spaced relationship around a longitudinal axis of rotation, said axis being the axis of rotation of an output shaft passing rotatably and sealably through apertures of respective first and second end plates of a housing within which the pistons and cylinders move as part of a rotatable rotor assembly secured to said output shaft, while the pistons are simultaneously movable reciprocably in the cylinders, cam follower means being associated with each piston and adapted to coact with undulating cam track means around the housing. Cyclical combustion of fuel in the cylinders imparts reciprocation to the pistons with resultant thrust against the cam track means so as to cause rotation of the rotor assembly and output shaft.