When the existence of several jurisdictions (countries, regions, or cities) is acknowledged, the possibility arises that citizens compare what obtains in their own jurisdiction to what obtains in others. These cross-jurisdiction or yardstick comparisons can have an effect on citizens’ support of incumbents (yardstick voting) and, as a consequence, an effect on governments’ decisions, making them interact (political yardstick competition proper). Both effects have been mainly studied in the context of federalism and decentralization, with the policy variables concerned being mostly fiscal (taxes and expenditures). In that relatively simple setting, the two effects have been confirmed empirically. This book aims to document and analyze that achievement and also to extend the analysis to broader settings in terms of jurisdictions and policy domains. It is mostly in that broader context, especially when national governments are involved, that the systemic implications of yardstick competition come to the fore. With regard to electoral or downward accountability, the mechanism tends to re-empower citizens by mitigating the disabling effects of information asymmetry. With regard to policy-making, yardstick competition represents a force, latent or actual, that constrains or influences the decisions of governments. The mechanism is simple but the political settings in which it operates, crucial for its understanding, are definitely complex. A methodological justification of how the matter is treated is placed at the end of the book.