Cities have been largely absent from the theory and legal doctrine of federalism, especially in the United States, where federalism is understood to refer to the constitutional relationship between states and between the states and the national government. This chapter argues that this is a mistake, both in theoretical and practical terms, and makes the case for a city-based federalism. The argument rests in part on a claim about the optimal scale for participatory, democratic government and in part on critiques of federalism as currently practiced in the U.S. My central claim is that U.S.-style, state-based federalism provides few of the benefits attributed to it because it is operating on the wrong scale. Cities are more likely to advance federalism’s stated aims. State restrictions on city power are undermining those same aims.