A multi-shaft engine is a type of piston internal combustion engine equipped with multiple crankshafts. The multi-shaft construction enables the realization of single-piston, two-piston (engine with counter-rotating pistons), and multi-piston engines.

A multi-shaft engine is always equipped with more than one crankshaft. According to the number of shafts, this motor is more precisely called, for example, a two-shaft motor, a three-shaft motor, a four-shaft motor, and so on.