Tuvalu (a low-lying Pacific island nation of around 11,000 people) is spearheading an unprecedented international effort to redefine the legal foundations of statehood in the face of existential climate threats. As rising sea levels place its physical territory at risk of becoming uninhabitable, the country is seeking to establish that sovereignty and nationhood can endure even if its land is largely submerged. The initiative carries major implications for international law and for other vulnerable island nations facing similar threats from climate change.