The French Forces of the Interior were French resistance fighters in the later stages of World War II. Charles de Gaulle used it as a formal name for the resistance fighters. The change in designation of these groups to FFI occurred as France's status changed from that of an occupied nation to one of a nation being liberated by the Allied armies. As regions of France were liberated, the FFI were more formally organized into light infantry units and served as a valuable manpower addition to regular Free French forces. In this role, the FFI units manned less active areas of the front lines, allowing regular French army units to practice economy of force measures and mass their troops in decisive areas of the front. Finally, from October 1944 and with the greater part of France liberated, the FFI units were amalgamated into the French regular forces continuing the fight on the Western Front, thus ending the era of the French irregulars in World War II.

The French Resistance was a collection of groups that fought the Nazi occupation of France and the collaborationist Vichy régime in France during the Second World War. Resistance cells were small groups of armed men and women who conducted guerrilla warfare and published underground newspapers. They also provided first-hand intelligence information, and escape networks that helped Allied soldiers and airmen trapped behind Axis lines. The Resistance's men and women came from many parts of French society, including émigrés, academics, students, aristocrats, conservative Roman Catholics, Protestants, Jews, Muslims, liberals, anarchists, communists, and some fascists. The proportion of French people who participated in organized resistance has been estimated at from one to three percent of the total population.