This article identifies and documents a trend in State practice over the past decade or so, regarding the impact of sea level rise on the lawfully determined limits of maritime zones and the existing maritime boundaries. It juxtaposes this development with the findings and recommendations of two committees of the International Law Association in 2012 and 2018 – the Committees on Baselines and Sea Level Rise – and examines the role played since 2019 by the International Law Commission. It explores the implications of emerging State practice for the interpretation of the rules and principles of the 1982 UN Law of the Sea Convention. It documents the complex interactions between the findings of international law scholarship and the evolution of State practice, and concludes that this interaction has played an important role in facilitating legal certainty and stability in the development of a response to this increasingly pressing international law issue.