Popular Fronts comprise broad coalitions of political and other groups, often made up of oppositioners or left wingers, and often united against particularly stringent circumstances. Being very broad, they can sometimes include centrist and liberal (or "bourgeois") parties and groups as well as socialists and communists ("working class" groups).

In addition to the general definition given above, the term "popular front" also has a specific meaning in the history of Europe during the 1930s, and Eastern Europe during the Cold War.

In response to the growing threat of fascism in the 1930s, the Communist Parties that were members of the Comintern (which was de facto controlled by Stalin) adopted a policy of forming broad alliances with almost any political party willing to oppose the fascists. These were called "popular fronts". Some popular fronts won elections and formed governments, as in France (Front Populaire), the Second Spanish Republic and Chile. Others never quite got off the ground (there were attempts in the United Kingdom to found a Popular Front between the Labour Party, the Liberal Party, the Independent Labour Party and the Communist Party, but they failed due to opposition from within the Labour Party).

Leon Trotsky and his supporters criticised this strategy, claiming that only united fronts could ultimately be progressive, and that popular fronts were useless because they included non-working class bourgeois forces such as liberals. Trotsky also argued that in popular fronts, working class demands are reduced to their bare minimum, and the ability of the working class to put forward its own independent set of politics is compromised. This view is now common to most Trotskyist groups. Left communist groups also oppose popular fronts, but they came to oppose united fronts as well.

After World War II, most Eastern European countries became de facto one-party states, but in theory they were ruled by coalitions between several different political parties who voluntarily chose to work together. For example, East Germany was ruled by a "National Front" of all anti-fascist parties and movements within parliament (Socialist Unity Party of Germany, Liberal Party, Peasants' Party, youth movement, trade unions, etc).

Coalitions called "Popular Fronts"

It should be noted that not all coalitions who use the term "popular front" necessarily are popular fronts, and not all popular fronts necessarily use the term "popular front" in their name. The same applies to united fronts.

• Popular Front for the Liberation of Palestine
• Popular Front (Spain)
• Popular Front (France)
• Belarusian Popular Front
• Azerbaijan Popular Front
• Popular Front (Mauritania)

Popular Fronts using other names

• Czechoslovakia - the National Front led by the Communist Party of Czechoslovakia
• East Germany - the National Front led by the Socialist Unity Party of Germany
• North Korea - the Democratic Front for the Reunification of the Fatherland led by the Workers' Party of Korea
• People's Republic of China - the United Front Work Department led by the Communist Party of China
• Poland - led by the Polish United Workers' Party
• Vietnam - the Fatherland Front led by the Communist Party of Vietnam