Rising sea levels threaten both the physical existence of several small island States and the legal existence of the fishery zones upon which they depend. Rising sea levels also threaten to erode the coastlines of continental States, thus determining the retreat of the maritime zones where those States harvested fish and extracted hydrocarbon resources. The 1982 United Nations Convention on the Law of the Sea (UNCLOS) divides the sea into zones under national jurisdiction (e.g., territorial sea and Exclusive Economic Zone). These zones are measured from the baseline, which is the limit of a State’s sovereignty over land on which the extent of maritime jurisdiction depends. Normally, the baseline runs along the coast of mainland territory and islands (Article 5 UNCLOS). If the coast is deeply indented, baselines can be straight lines connecting fixed points on the coast (Article 7 UNCLOS). By changing the shape of coastlines, sea-level rise complicates the UNCLOS legal framework. UNCLOS seems to foresee this eventuality by providing for ambulatory baselines that change as the coastline changes. Yet, States have been reluctant to accept that, owing to sea-level rise, they may lose sovereign rights in maritime areas under their jurisdiction. Certain States have passed legislation to make their baselines permanent. This sea-level-rise-driven practice, which is mostly undocumented, urges us to re-think UNCLOS’ notion of “baseline”. Moreover, certain States have been fortifying existing maritime features to prevent their disappearance. The question is whether fortifications are compatible with the notion of “island” under Article 121 UNCLOS as a “naturally formed area of land”. Because of their foundational character in the law of the sea, re-thinking these notions will be a theoretical paradigm shift for the field. In practice, this project will impact the South China Sea dispute, as the maritime claims of the relevant States, including China, rest on the character of fortified maritime features as “islands”. The PI’s collaborator will be Dr. Nilüfer Oral, Co-chair of the International Law Commission’s Study Group on Sea-level Rise. The project will result in at least two journal articles and be disseminated to its intended audience in three ways: (i) a conference in Hong Kong and intended for East Asian scholars and policymakers; (ii) a workshop in Geneva during the 2025 session of the International Law Commission, intended for members of the Commission; (iii) a publicly-accessible online database on State practice (i.e., manifestation of State conduct) on sea-level rise.