A popular front is a broad coalition of different political groupings, often made up of leftists and centrists. Being very broad, they can sometimes include centrist and liberal (or "bourgeois") forces as well as socialist and communist ("working-class") groups. Popular fronts are larger in scope than united fronts, which contain only working-class groups.

In addition to the general definition, the term "popular front" also has a specific meaning in the history of Europe and the United States during the 1930s, and in the history of Communism and the Communist Party. During this time, the "popular front" referred to the alliance of political parties in France aimed at resisting Fascism. The term "national front", similar in name but describing a different form of ruling, using ostensibly non-Communist parties which were in fact controlled by and subservient to the Communist party as part of a "coalition", was used in Central and Eastern Europe during the Cold War.

Not all coalitions who use the term "popular front" meet the definition for "popular fronts", and not all popular fronts use the term "popular front" in their name. The same applies to "united fronts".