A motorcycle engine is an engine that powers a motorcycle. Motorcycle engines are typically two-stroke or four-stroke internal combustion engines, but other engine types, such as Wankels and electric motors, have been used.

Although some mopeds, such as the VéloSoleX, had friction drive to the front tire, a motorcycle engine normally drives the rear wheel, power being sent to the driven wheel by belt, chain or shaft. Historically, some 2,000 units of the Megola were produced between 1921 and 1925 with front wheel drive, and the modern Rokon, an all terrain motorcycle with both wheels driven, has been produced since 1960.

Most engines have a gearbox with up to six or even 7 ratios. Reverse gear is occasionally found on heavy tourers, for example the Honda GL1600, and sidecar motorcycles, such as the Ural. The rider changes gears on most motorcycles using a foot-pedal and manual clutch, but early models had hand-levers. More recently, some have automatic or semi-automatic gearboxes, and some using CVT transmission.

Outside the United States, engine capacities typically ranged from about 50 cc to 650 cc; but in Europe since 1968 motorcycles with larger capacities have become common, ranging as high as the Triumph Rocket 3's 2,300 cubic centimetres (140 cu in) engine. In the United States, V-twin engined motorcycles with capacities of 850 cc or more have been the norm since the 1920s.