Libertarianism is a theory of justice that places significant moral weight on exclusive property rights. On this basis, many libertarian philosophers, from Robert Nozick to Michael Huemer, criticize any form of income redistribution. Ironically, some libertarians, following Philippe Van Parijs, Matt Zwolinski, and Charles Murray, have supported the introduction of an unconditional basic income. This essay seeks to prove that this support is not just a political compromise. By contrast, libertarian justice advocates have a strong moral basis for supporting income (...) redistribution in the form of unconditional cash payments. This essay explores one such reason, the Lockean proviso. The Lockean proviso is a moral requirement for the appropriation of unowned resources to leave “enough and as good” for others. There are many interpretations of the Lockean proviso, but the most ambitious are the egalitarian proviso and the sufficiency proviso. Each of them, but for different reasons, requires the introduction of a basic income. The egalitarian proviso establishes the equal rights of all people to natural resources, and therefore requires that all benefits from the ownership of natural resources be shared egalitarianly — in the form of unconditional equal payments. The sufficiency proviso establishes some threshold of sufficiency, and then imposes a restriction on exclusive property rights so that they can’t prevent redistribution in order to raise all people to the threshold of sufficiency. However, while both provisos require a basic income, they diverge on three important dimensions in assessing this basic income: applicability, taxable base, and amount of cash payments. (shrink)