Abstract: The invention relates to an internal combustion engine having separate rotary compression and expansion sections and a combustion chamber (16) having valved inlet and outlet ports (21,22) communicating with the compression and expansion chambers respectively. Each section is a rotary device comprising a first rotor (14b) rotatable about a first axis (11) and having at its periphery a recess (R) bounded by a curved surface; and a second rotor (14a) counter-rotatable to the first rotor (14b) about a second axis (10), parallel to the first axis (11), and having a radial lobe (P) bounded by a curved surface, the rotors intermeshing whereby, on rotation thereof, a transient chamber of progressively increasing (expansion section) or decreasing (compression section) volume is defined between them.