This book examines national power in the contemporary international system through an empirically grounded and theoretically integrated framework. Rooted in the trans-structural approach, it builds upon the theory of national-international power and consolidates the World Power Index (WPI) as a comprehensive measure of state capabilities across material, semimaterial, and immaterial dimensions. The volume applies the WPI to measure, classify, and compare national power across the Global North and Global South, analyzing its implications for the provision of global public goods, health equity, artificial intelligence, ecological asymmetries, and the strategic role of elite sport in revealing national power and generating soft power. More than a collection of studies, this book establishes the WPI as a reference framework for the study of national power and the international geostructure, offering scholars and policymakers a systematic foundation for interpreting the global power shift.