This Essay surveys dormant foreign Commerce Clause doctrine to determine what limits it places on state taxation of international income, including both income earned by foreigners in a U.S. state and income earned by U.S. residents abroad. The dormant Commerce Clause similarly limits states’ powers to tax interstate and foreign commerce; in particular, it forbids states from discriminating against interstate or international commerce. But there are differences between the interstate and foreign commerce contexts, including differences in the nationality of affected taxpayers and differences in the impact of state taxes on federal tax and foreign-relations goals. Given current Supreme Court doctrine, we provide states guidance as to how to conform their regimes for taxing international income to constitutional requirements.