A red star, five-pointed and filled, is a symbol that has often historically been associated with communist ideology, particularly in combination with the hammer and sickle, but is also used as a purely socialist symbol in the 21st century. It has been widely used in flags, state emblems, monuments, ornaments, and logos. A golden star or yellow star is also a closely-associated symbol to the red star in the context of contemporary China and Vietnam, similarly representing socialism, communism, and national communism.

Some former Warsaw Pact nations have passed laws banning it, describing it as a symbol of far-left totalitarian ideology. The red star has also been used in a non-communist context and before the emergence of this movement, in symbols of countries and states since the 19th century. It appears for example on the flags of New Zealand and the U.S. state of California. The red star has also been used as logo by private agencies and corporations, such as the oil brand Texaco and the beer Heineken.

The star's origins as a symbol of communist mass movements dates from the time of the Bolshevik Revolution and the Russian Civil War, but the precise first use remains unknown. The red star as a symbol of the Red Army was proposed by the Military Collegium for the organization of the Red Army and the creator of the Red Star emblem was the Bolshevik commander of the Petrograd Military District, Konstantin Eremeev. On the other hand, one account of the symbol's origin traces its roots to the Moscow troop garrison toward the end of World War I. At this time, many troops were fleeing from the Austrian and German fronts, joining the local Moscow garrison upon their arrival in the city. To distinguish the Moscow troops from the influx of retreating front-liners, officers gave out tin stars to the Moscow garrison soldiers to wear on their hats. When those troops joined the Red Army and the Bolsheviks they painted their tin stars red, the color of socialism, thus creating the original red star.

The red star was used in communist media as early as in 1908 with the publication of the novel Red Star by Bolshevik revolutionary Alexander Bogdanov, which describes a technologically advanced communist civilization on Mars.

Another claimed origin for the red star relates to an alleged encounter between Leon Trotsky and Nikolai Krylenko. Krylenko, an Esperantist, wore a green-star lapel badge; Trotsky inquired as to its meaning and received an explanation that each arm of the star represented one of the five traditional continents. On hearing that, Trotsky specified that soldiers of the Red Army should wear a similar red star.

One interpretation sees the five points as representing the five fingers of the worker's hand, as well as the five populated continents (counting the Americas as one). A lesser-known suggestion is that in communist symbolism, the five points on the star were intended to represent the five social groups that would lead Russia to communism: the youth, the military, the industrial labourers, the agricultural workers or peasantry and the intelligentsia. In Soviet heraldry, the red star symbolized the Red Army and military service, as opposed to the hammer and sickle, which symbolized peaceful labour.^{[citation needed]}

Regardless of the star's exact origin, it was incorporated into the Red Army's uniforms and heraldry as early as 1918.

Shortly before the founding of the Soviet Union, in mid-March 1916 the U.S. Army Signal Corps' aviation section used the red star for the national insignia for U.S. aircraft on the aircraft of the Signal Corps' 1st Aero Squadron during the Pancho Villa Expedition to apprehend the Mexican revolutionary Pancho Villa.