The primary contribution of this book has less to do with any specific theoretical or empirical result and more to do with the attention it draws to an important but heretofore overlooked dimension of American politics: the vertical dimension. Where conventional horizontal theories suggest that the multiplication of jurisdictions enhances competition and efficiency, I contend that the proliferation of vertically overlapping jurisdictions is likely to have just the opposite effect. In large part, the failure of conventional theories to recognize the vertical dimension of governmental competition stems from the fact that jurisdictional layering on a large scale–that is, beyond the traditional federal-state-local overlay–is a relatively recent phenomenon; the majority of special-purpose jurisdictions that exist today were created after World War II. The workhorse theories of local political economy–beginning with Tiebout in 1956–have largely failed to keep pace with the institutional innovations that made vertically overlapping single-function jurisdictions the most numerous and fastest-multiplying American governments. Although single-function jurisdictions now outnumber and outspend all cities, and have more civilian employees than the federal government, scholars have yet to offer a working theory of their politics, much less a rigorous empirical investigation of such a theory. My aim in this book has been to begin filling that gap by providing a political theory of special-function government and testing that theory with comprehensive data and careful analysis.