Abstract: A rotary piston internal combustion engine, includes a common housing; a stationary hollow hub; two rotary piston systems in the housing, each system including at least one piston rotor having partial cylindrical areas and front areas, the second rotary piston system including two piston rotors revolving symmetrically about a common axis and about the hub; bearing means for mounting the two rotary piston systems on parallel axes in the housing such that the piston rotors mesh with one another during opposite rotation of the two rotary piston systems, paths of movement of the piston rotors are annular and overlap one another in a penetration region of the housing, the partial cylindrical areas of each piston rotor of the first rotary piston system, during rotation thereof, forming a sealing gap of great depth alternately with the housing, and with the second rotary piston system or the hollow hub, and the front ends of the piston rotors of the second rotary piston system working together with front ends of at