The Lancia Flat-4 engine is an aluminum, pushrod, and later overhead camshaft, flat-four (boxer) engine made by Lancia, initially for the Flavia, from 1960 through 1984. Though it was designed as a pushrod engine, it was advanced for the time. The pushrod version of the Lancia boxer was only ever used in the Flavia, and its derivatives including the Lancia 2000. In 1976, a new overhead cam engine based on a similar layout was designed and brought into production in 2 and 2.5-litre displacements for the Gamma.

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.