The 1923 Treaty of Lausanne marked a decisive moment in international diplomacy, laying the foundations for stability and peaceful coexistence in Southeast Europe and the Middle East. By completing the transition from empire to nation-state, the treaty established internationally recognized borders, restored sovereignty, and replaced prolonged conflict with a durable legal framework that continues to underpin regional peace a century later. This volume brings together leading scholars to examine the negotiations, legal innovations, and long-term significance of the Treaty of Lausanne. It highlights the role of the major powers—namely Britain, France, Italy, and Japan—alongside regional actors such as Greece, Romania, the Kingdom of Serbs, Croats and Slovenes, and the newly established Republic of Turkey. The book also explores the Treaty’s broader international resonance, including its implications for Asian countries such as India and China. Particular attention is devoted to the development of minority protections under international law, and the safeguarding of the Ecumenical Patriarchate as a vital spiritual and institutional presence. One hundred years on, the Treaty of Lausanne remains one of the principal peace instruments shaping political order, legal continuity, and interstate relations in the region. By combining legal analysis with diplomatic history, this volume offers a constructive reassessment of Lausanne’s enduring contribution to international stability and the foundations of the modern international order.