The Treaty of Lausanne, signed on 24 July 1923, established the modern legal and geopolitical framework of the Eastern Mediterranean. Replacing the Treaty of Sèvres, it recognized the sovereignty of the Republic of Turkey, defined borders with Greece and neighbouring states, addressed minority rights, and regulated, although through a separate treaty, population exchanges (under a separate Convention) and territorial claims. Key provisions renounced Turkish sovereignty over Cyprus and the Dodecanese, and established rules for the Turkish Straits. While some claims have suggested a 2023 “expiration”, the Treaty remains legally binding unless superseded by subsequent agreements. Lausanne contributed to regional stability and shaped Greek-Turkish relations, but it also left enduring human consequences: Armenians lacked autonomy, Kurds remained stateless, and the subsequent population exchanges caused large-scale displacement. Contemporary disputes over Aegean islands and maritime zones illustrate the ongoing geopolitical relevance of the Treaty. The legacy of Lausanne highlights the enduring importance of international legal frameworks in managing sovereignty, minority rights, and regional stability a century after its signing.