Abstract: An oscillating piston machine, specifically adapted for use as an Internal Combustion Engine, preferably for two stroke operation, or alternatively, specifically adapted for use as a compressor, or alternatively as a pump, or alternatively as a fluid driven motor, comprising a plurality of arcuate, rectangular faced, double acting, oscillating pistons, symmetrically secured to an oscillating disc supported by an oscillating flange, mounted on bearings on a long central shaft fixed to a robust wall of a crankcase housing; the oscillating flange face contains a gudgeon pin linked by a single connecting rod to the crank pin of an output crankshaft, and mounted in bearings on the same wall. Rotation of crank shaft produces oscillating motion of flange, disc, and pistons. The pistons oscillate within an annular enclosure formed by the oscillating disc, and a stationary inner concentric cylinder, bolted to a stationary disc, bolted to an outer concentric cylinder, bolted to the crankcase housing.