Property is theft! (French: La propriété, c'est le vol!) is a slogan coined by French anarchist Pierre-Joseph Proudhon in his 1840 book What is Property? Or, an Inquiry into the Principle of Right and of Government.

If I were asked to answer the following question: What is slavery? and I should answer in one word, It is murder!, my meaning would be understood at once. No extended argument would be required . . . Why, then, to this other question: What is property? may I not likewise answer, It is robbery!, without the certainty of being misunderstood; the second proposition being no other than a transformation of the first?

—Pierre-Joseph Proudhon, What is Property?

By "property," Proudhon referred to the concept originated in Roman law of the sovereign right of property—the right of the proprietor to do with his property as he pleases, "to use and abuse," so long as in the end he submits to state-sanctioned title, and he contrasted the supposed right of property with the rights (which he considered valid) of liberty, equality, and security.