The political slogan "Workers of the world, unite!" is one of the rallying cries from The Communist Manifesto (1848)^[1][2][3][4] by Karl Marx and Friedrich Engels (German: Proletarier aller Länder, vereinigt Euch!, literally 'Proletarians of all countries, unite!',^[5] but soon popularised in English as "Workers of the world, unite! You have nothing to lose but your chains!").^{[5][note 1]} A variation of this phrase ("Workers of all lands, unite") is also inscribed on Marx's tombstone.^[7] The essence of the slogan is that members of the working classes throughout the world should cooperate to defeat capitalism and achieve victory in the class conflict.

Five years before The Communist Manifesto, this phrase appeared in the 1843 book The Workers' Union by Flora Tristan.^[8]

The International Workingmen's Association, described by Engels as "the first international movement of the working class" was persuaded by Engels to change its motto from the League of the Just's "all men are brothers" to "working men of all countries, unite!".^[9] It reflected Marx's and Engels' view of proletarian internationalism.

The phrase has overlapping meanings: first, that workers should unite in unions to better push for their demands such as workplace pay and conditions;^{[10][better source needed]} secondly, that workers should see beyond their various craft unions and unite against the capitalist system;^[11] and thirdly, workers of different countries have more in common with each other than workers and employers of the same country.

The phrase was used by the Industrial Workers of the World (IWW) in their publications and songs^[12][13] and was a mainstay on banners in May Day demonstrations. The IWW used it when opposing World War I in both the United States^[13] and Australia.^[14]

The slogan was the Soviet Union's state motto (Пролетарии всех стран, соединяйтесь!; Proletarii vsekh stran, soyedinyaytes'!) and it appeared in the State Emblem of the Soviet Union. It also appeared on 1919 Russian SFSR banknotes (in Arabic, Chinese, English, French, German, Italian and Russian),^[15] on Soviet ruble coins from 1921 to 1934^[16] and was the slogan of Soviet newspaper Pravda.^[17]

Some socialist and communist parties continue using it.^{[18][failed verification]}

In the first Swedish translation of The Communist Manifesto, published in 1848, the translator Pehr Götrek substituted the slogan with Folkets röst, Guds röst! (i.e. Vox populi, vox Dei, or "The Voice of the People, the Voice of God"). However, later translations have included the original slogan.^[19]

The guiding motto of the 2nd Comintern congress in 1920, under Lenin's directive, was "Workers and oppressed peoples of all countries, unite!".^[20] This denoted the anti-colonialist agenda of the Comintern, and was seen as an attempt to unite racially-subjugated black people and the global proletariat in anti-imperialist struggle.^[20]

This section does not cite any sources. (October 2022)

This slogan was used by several socialist states and communist parties as their official motto.