A communist front (or a mass organization in communist parlance) is a political organization identified as a front organization, allied with or under the effective control of a communist party, the Communist International or other communist organizations. It is a structure used by Communist and left-wing parties to intervene in broader political movements. They attracted politicized individuals who were not party members but who often followed the party line and were called fellow travellers.

Vladimir Lenin originated the idea in his manifesto of 1902, What Is to Be Done? Since the party was illegal in Russia, he proposed to reach the masses through "a large number of other organizations intended for wide membership and, which, therefore, can be as loose and as public as possible". Generally called "mass organizations" by the communists themselves, these groups were prevalent from the 1920s through the 1950s, with their use accelerating during the popular front period of the 1930s. The term has also been used to refer to organizations not originally communist-controlled which after a time became so such as the American Student Union. The term was especially used by anti-communists during the Cold War.

Mao Zedong broke bitterly with the Soviet Union in the late 1950s. He set up a network of pro-Chinese, anti-Soviet parties and communist fronts that directly challenged the pro-Soviet organizations.

Under the leadership of Grigory Zinoviev in the Kremlin, established fronts in many countries in the 1920s and after. To coordinate their activities the Communist International (Comintern) set up various international umbrella organizations (linking groups across national borders), such as the Young Communist International (youth), Profintern (trade unions), Krestintern (peasants), International Red Aid (humanitarian aid), Red Sport International (organized sports), etc. In Europe, front organizations were especially influential in Italy and France, which in 1933 became the base for Communist front organizer Willi Münzenberg. These organizations were dissolved the late 1930s or early 1940s.

Communist fronts typically attracted well-known and prestigious artists, intellectuals and other "fellow travelers" who were used to advance Party positions. Often they came to the USSR for closely controlled tours, then returned home to praise the future as revealed in the Soviet experiment.

According to Kennedy (1957), after the war, especially as the Cold War took effect around 1947, the Kremlin set up new international coordination bodies including the World Federation of Democratic Youth, International Union of Students, World Federation of Trade Unions, Women's International Democratic Federation, and the World Peace Council. Kennedy says the, "Communist 'front' system included such international organizations as the WFTU, WFDY, IUS, WIDF and WPC, besides a host of lesser bodies bringing journalists, lawyers, scientists, doctors and others into the widespread net."

The International Federation of Resistance Fighters – Association of Anti-Fascists (FIR) was designated by government agencies as a communist-influenced organization.

The World Federation of Scientific Workers (WFSW) is an international federation of scientific associations. It was a Cold War-era Communist front. The group was composed of scientists who supported communism. The federation opposed nuclear tests conducted by the United States.