A Hemi engine (from hemisphere) is an internal-combustion engine in which the combustion chambers are of hemispherical form. The term "Hemi engine" is a trademark of Chrysler Corporation, though they were neither the hemi engine's inventors nor the first to commercialize hemi engines.

Hemispherical combustion chambers, which had been used for centuries in mortars and cannon , were introduced on some of the very earliest automotive engines, shortly after proving the concept of internal combustion engines themselves.