Abstract: A concentric rotary engine of the internal combustion type is provided which includes a rotor concentrically disposed within a hollow rotor housing. The rotor, which has a perimetrical cam surface defining lobe portions separated by pocket portions, is in slidable, sealable and rotatable engagement with the inner surface of the rotor housing. A power transfer shaft is secured to the rotor and extends beyond the housing. The engine is provided with one or more operative sections each of which includes a leading gate system, a trailing gate system and a combustion chamber disposed therebetween. The operative section, in cyclical sequence, cooperates with the rotor lobe and pocket portions together with intake and exhaust passage systems to effect the engine cycle in respect of the intake, compression, combustion, expansion and exhaust steps.