This book analyzes the international relations of Mexico and the two most important sub-state governments of the United States, California and Texas. It explains why and how these two states conduct their international relations (IR) with Mexico and the world, and how national authorities and local governments coordinate in the definition and implementation of their international policies. Expert contributors from across the Americas offer a historical and current analysis, exploring which areas of cooperation-trade, investment, border cooperation, energy, migration-matter most. They also consider the institutional and legal bases of Mexican and U.S. states’ international relations, the changing nature of the U.S. federal system, the impact on international partners, the role of Latinos and the future of paradiplomacy in the region. The book will be of interest to scholars and students of International Relations, comparative politics, diplomacy, foreign policy, governance, and federalism, as well as business people, social leaders, and practitioners of diplomacy and paradiplomacy around the world.