The 1951 Grand Prix motorcycle racing season was the third F.I.M. Road Racing World Championship Grand Prix season. The season consisted of eight Grand Prix races in five classes: 500cc, 350cc, 250cc, 125cc and Sidecars 500cc. It began on 8 April, with Spanish Grand Prix and ended with Nations Grand Prix on 9 September. As of 2022, this is the most recent season the premier class was won by a non-Japanese or non-Italian constructor.

The 1950 Grand Prix motorcycle racing season was the second F.I.M. Road Racing World Championship Grand Prix season. The season consisted of six Grand Prix races in five classes: 500cc, 350cc, 250cc, 125cc and Sidecars 600cc. It began on 10 June, with Isle of Man TT and ended with Nations Grand Prix on 10 September.