A libertarian theory of justice holds that persons are self-owners and have the Hohfeldian moral power to justly acquire property rights in initially unowned external resources. Different variants of libertarianism can be distinguished according to their stance on the famous Lockean proviso. The proviso requires, in Locke’s words, to leave ‘enough and as good’ for others, and thus specifies limits on the acquisition of property. Left-libertarians accept an egalitarian interpretation of the proviso, ‘right-libertarians’ either reject any kind of proviso or (...) accept rather weak versions of it. In be-tween there is room for moderate interpretations of the proviso, and in particular for a sufficientarian interpretation: a ‘sufficiency proviso.’ The resulting theory of justice can be called ‘moderate libertarianism.’ In this article I make a case for moderate libertarianism, so understood. I argue that moderate libertarianism has advantages over both left- and right-libertarianism because it better coheres with the most plausible rationale for endorsing a libertarian theory of justice in the first place. (shrink)