Ludovic-Oscar Frossard, also known as L.-O. Frossard or Oscar Frossard, was a French socialist and communist politician. He was a founding member in 1905 and Secretary-General of the French Socialist Party (SFIO) from 1918 to 1920, as well as a founding member and Secretary-General of the French Communist Party (PCF) from 1920 to 1922.

The French Communist Party is a communist party in France. The PCF is a member of the Party of the European Left, and its MEPs sit with The Left in the European Parliament – GUE/NGL group.