Mutualism is the anti-capitalist anarchist tradition Pierre-Joseph Proudhon founded in mid-nineteenth-century France. Economic justice, on its account, requires neither state coercion nor capitalist ownership, but the voluntary association of producers exchanging the products of their own labor on equitable terms.
What Is Property? (1840) introduced the claim that property is theft. The target was not personal possession but absentee ownership, and the rent, interest and profit by which Proudhon argued capital captures what labor produces. His constructive program centered on producer cooperatives, mutual credit institutions lending at cost instead of at interest, and contractual federation replacing the state as the coordinator of large-scale economic life. He tried to found a People's Bank on these lines in 1849. It failed within months.
Mutualism is the historical root of market socialism. It was the first tradition to argue that markets and competition could be kept while ownership was decentralized to those who actually labor, an insight twentieth-century market socialists adapted to industrial scale. It differs from individualist anarchism in its emphasis on cooperative federation and its direct attack on wage labor, since mutualists treat the employer-employee relation itself as the central injustice. Individualist anarchists care more about sovereignty against any external authority and prescribe less about economic form.
Proudhon was also the target of the most famous polemic in socialist history. Marx's The Poverty of Philosophy (1847) dismissed the mutualist program as petty-bourgeois nostalgia for small proprietorship in an age of large-scale industry, an objection mutualists have been answering ever since. Proudhon's own writings on Jews and on women are ugly enough that the tradition's modern adherents generally repudiate them instead of contextualizing them.