Scholars and courts recognize that the federal government uses its broad spending power to enlist states in achieving federal goals, thereby expanding the federal government’s reach beyond the areas enumerated for it in the Constitution. Previously underappreciated, however, is that the federal government can achieve similar ends-it can regulate the states and private parties-through its potentially equally broad taxing power. This Article draws on the spending power literature to illuminate the analogous federalism concerns raised by expansive use of the taxing power. For example, by crowding out state regulation of similar policy areas, federal tax regulation may limit policy diversity and hinder regulatory competition both among the states and between the states and the federal government. But this Article also identifies important differences between taxation and grants that suggest that federal tax regulation represents less of a federalism threat than do conditional grants to the states. For example, because federal tax incentives neither contractually bind states to follow federal policy nor expend state legislative and administrative resources in enacting and enforcing federal policy, states may remain freer under tax incentives than grants to enact concurrent or contrary policies.