We develop a political economy model of intergovernmental transfers. Vertical fiscal balance occurs in a federation when the ratio of the marginal benefit of the public services provided by the federal and provincial governments is equal to their relative marginal costs of production. With majority voting in national elections, the residents of a «pivotal province» will determine the level of transfers such that the residents of that province achieve a vertical fiscal balance in spending by the two levels of government. We test the predictions of the model using Canadian time series data and cross-section data for nine federations.