Abstract: An opposed piston internal combustion engine comprises an output shaft, at least one cylinder, at least one pair of first and second opposed pistons slidable in said cylinder, a first cam connected to the output shaft and a first cam follower assembly connecting the first piston to the first can, a second cam connected to the output shaft and a second cam follower assembly connecting the second piston to the second cam, an intake valve comprising a slide valve obtained by first piston covering and uncovering an intake port provided in a sidewall of the cylinder at a first end of the cylinder, and an exhaust valve comprising a slide valve obtained by the second piston covering and uncovering an exhaust port provided in the sidewall of the cylinder at a second opposite end of the cylinder, the first and second cams cooperating to provide a cycle of relative movements between the pistons and of valve actions giving rise to five cycles of (i) intake, (ii) compression, (iii) expansion, (iv) exhaust, and (v) return