This updated and revised second edition provides a comprehensive scholarly framework for analyzing the theory and history of international law. Featuring an array of legal and interdisciplinary analyses, it focuses on those theories and developments that illuminate the central and timeless basic concepts and categories of the international legal system, highlighting the interdependency of various aspects of theory and history and demonstrating the connections between theory and practice. With contributions from renowned experts, this Research Handbook explores the essence and development of international legal theory, taking account of the key shifts and advances since the era of classical legal scholarship. Contributors examine several major areas of international law in depth, before transferring their focus to the history of international law from the medieval period up to the present day. Coverage has been expanded to include analysis of the origins of and Eurocentric narratives surrounding the present system, and to discuss significant developments of the 21st century. Scholars and students of international law and politics looking for an in-depth understanding of the current international legal system and its history will find this Research Handbook to be crucial reading. Its theoretical approach will also be of interest to legal theorists, as well as researchers in ethics and philosophy.