The Riley RM Series is an executive car which was produced by Riley from 1945 until 1955. It was the last model developed independently by Riley prior to the 1952 merger of Riley's still new owner Nuffield, with Austin to form BMC. The RM series was originally produced in Coventry, but in 1949 production moved to the MG works at Abingdon. The RM models were marketed as the Riley 1½ Litre and the Riley 2½ Litre.

There were four types of RM vehicles produced. All used Riley engines with four cylinders in-line, hemispherical combustion chambers and twin camshafts mounted high at the sides of the cylinder block.

The RMA was a large saloon, and was replaced by the RME. Both used a 1.5 L (1496 cc) 12 hp (RAC Rating), developed before WWII.

The RMB was a longer car: it was replaced by the RMF. Both cars used a larger engine, new in 1937, a 2.5 L 16 hp (RAC Rating) "Big Four".

The RMC and RMD were limited-production cars, an open 2 or 3-seater Roadster and a 4-seater Drophead.

The Riley Pathfinder was the RMH and the last saloon to have the Riley Big Four engine.