the oldest of the French political parties, officially founded in 1901 but tracing back to “radical” groups of the 19th century. Traditionally a centrist party without rigid ideology or structure, it was most prominent during the Third Republic (to 1940) and the Fourth Republic (1945–58) but continued to be influential during the Fifth Republic (from 1958).

The first French “radical” party was active in the Revolution of 1848. In the 1870s, the more reformist wing of the Republican Party, led by Georges Clemenceau among others, became known as the Radicals. The party played an important part in administrations of the late 19th and early 20th century. In the 1930s the Radicals began to lose ground. Although they won control of the government in the 1932 election, the Socialist Party won the popular vote. In 1936 the Radicals were reduced to participation in the Socialist Party's coalition government, Léon Blum's Popular Front.

After World War II the Radicals' popularity further declined. In the 1940s and early 1950s, they formed with other groups the Rassemblement des Gauches Républicaines (RGR; “Assembly of Republican Leftists”), which never won more than 11 percent of the vote in legislative elections. Until 1958, however, the Radicals played disproportionately important roles in the governments of the Fourth Republic, since party fragmentation in the National Assembly made the politically central Radical group important.

Under General Charles de Gaulle's Fifth Republic, founded in 1958, the Radicals continued both to lose votes and to hold key political positions. In 1965 the Radicals supported François Mitterrand, the unsuccessful presidential candidate of the all-left Fédération de la Gauche Démocrate et Socialiste (“Federation of the Democratic and Socialist Left”). Thereafter it participated in various centrist, centre-left, and centre-right coalitions.