An internal combustion engine includes a piston dividing a cylinder into first and second variable volume chambers on either side thereof. One chamber admits and compresses air which is delivered to another chamber for combustion. The other chamber admits combustion gasses, causing the piston to translate in the cylinder. In one embodiment, combustion of fuel occurs in a combustion chamber separate from the first and second variable volume chambers. In one embodiment, the translation of the piston effects movement of a connecting rod connected to an output shaft. In another embodiment, the piston is mounted on an output shaft and translation of the piston causes the piston to rotate, thus effecting rotation of the output shaft.