An unconditional basic income is a cash transfer paid to every individual within a political community, without means-test or work requirement. Although this radical idea was first formulated two centuries ago, it continues to generate controversy among political philosophers. Following lines of argument ranging from libertarianism to Marxism, its advocates claim that it allows for the fair distribution of a share of our collective wealth, while ensuring the material conditions of freedom. Opponents, on the other hand, argue that such a measure would be unjust, for instance because it violates a well-established norm of reciprocity by allowing non-working individuals to exploit productive people. Even if the political chances of basic income remain rather slim, this controversy offers a particularly revealing perspective on the ongoing debates surrounding welfare reform in industrialized countries.