This paper empirically investigates the underlying causes of expenditure decentralization, based on the predictions of a new political economy model of partial fiscal decentralization. Under shared expenditure responsibility, the degree of decentralization is endogenous and depends on the relative political conditions prevailing at each level of government. Our empirical results from a panel of democracies support the relevance of political factors as determinants of fiscal decentralization. The relationship between central government electoral strength and both expenditure and revenue centralization emerges as nontrivial and non-linear. Political forces at the central government level driving centralization up and down appear to coexist.