The Subaru EA engine is a series of automobile internal combustion engines manufactured by Subaru, a division of Fuji Heavy Industries. All EA series engines are of a flat-4 design, and have always been water cooled.

A flat-four engine, also known as a horizontally opposed-four engine or boxer engine, is a four-cylinder piston engine with two banks of cylinders lying on opposite sides of a common crankshaft. The most common type of flat-four engine is the boxer-four engine, each pair of opposed pistons moves inwards and outwards at the same time.