This article quantifies personal income tax compliance by regions for the first time in Spain and identifies the factors explaining differences in tax compliance between regions, an aspect that has scarcely been analyzed in the literature. To this end, and in addition to the dynamic and spatial components considered by Alm and Yunus, this article considers the variables included in the classical tax evasion model of Allingham and Sandmo, as well as tax morale and political-institutional variables, including those linked to the country’s fiscal decentralization. The results obtained confirm, on one hand, those reached in the very extensive literature studying tax evasion from the individual perspective (including the importance of the dynamic element) and, on the other, the relevance of the spatial component in explaining tax compliance, so that greater or lesser tax compliance is partly explained by factors such as the tax behavior of neighbors or how those neighbors are treated by the public sector.