In this article I present the normative case for global tax governance. I argue that, contrary to an influential part of the literature, national tax policy choices cause significant externalities for other nation states. Focusing in business taxation, I show that tax competition undermines the integrity and distributive principles of domestic tax systems, and aggravates the inequality between ... [Show full abstract] developed and developing countries. Further, I demonstrate that the effects of international tax competition are unjust irrespective of whether a globalist or less demanding internationalist perspective on justice is adopted. The minimum requirement of justice is to devise global rules which ensure that national tax systems remain capable to implement distributive justice as they see fit. Finally, I present and discuss a concrete proposal for the global governance of business tax competition, namely, unitary taxation with formula apportionment.