The Riley 12/4, or from 1936 the Riley 1½-litre, is a range of cars made from 1935 to 1938 by the British Riley company available with saloon, touring, and sports/racing coachwork, The car is powered by a four-cylinder 1,496 cc (91.3 cu in) "12/4 Engine" with one or two Zenith carburettors.

Designed by Hugh Rose, it was based on the Riley Nine engine but with some significant changes including the cylinder block and crankcase being cast as one unit.

It was advanced for its day with twin camshafts mounted high in the engine block, cross flow head on some versions, and Zenith or twin SU carburettors.

Production of the engine continued until 1955 and also powered cars sold under these model names in these model years: The chassis had half-elliptic leaf springs all round and drive was to the rear wheels through either a four-speed preselector or manual gearbox.

[1] At launch three body styles were available: the Kestrel 4 light fastback saloon, the Falcon saloon and the Lynx open tourer.