This chapter examines the roles of both: Italy and Romania during the negotiations about the settlement of the Treaty of Lausanne, which was signed in 1923, and has often been interpreted as cornerstone of the post-Ottoman international order. While Italy sought to consolidate its Mediterranean presence, particularly through the question of the Dodecanese Islands, Romania approached Lausanne as an opportunity to reinforce its security in the Black Sea region and to legitimize its minority policies within an emerging international legal framework. This study analyzes how both states employed international law. On the one hand, Italy is emphasizing doctrines of effective occupation and treaty revision, on the other hand, Romania is advocating universalization of minority protection and freedom of navigation. Both countries tried to pursue divergent yet complementary objectives. The findings suggest that Lausanne not only settled immediate territorial disputes but also functioned as a testing ground of interwar international law, where sovereignty, minority rights, and multilateral treaty-making were tested and institutionalized. By comparing Italy’s pursuit of prestige and territorial influence with Romania’s quest for legal legitimacy and security, the article highlights the dual nature of international law in the interwar period: a normative system and, simultaneously, a tool of power politics.