This article examines the substantive and organizational dimensions of transboundary cooperation and urban paradiplomacy in addressing climate change adaptation. It explores how cities establish international linkages and employ multi-level governance mechanisms to anticipate and respond to climate-related risks. The study is motivated by the growing prominence of climate paradiplomacy, the intensification of regional adaptation policies in Russia, and the increasing vulnerability of coastal cities to the impacts of a changing climate. Empirical analysis focuses on adaptation strategies and action plans from nine coastal cities of the Baltic region, encompassing ten countries. Applying a comparative matrix-based discourse analysis, the study traces how international and regional organizations, along with city networks such as the Global Covenant of Mayors for Climate and Energy, the Union of the Baltic Cities, and ICLEI Europe, shape local adaptation frameworks and implementation practices. The findings show that while all examined cities have entered the implementation phase of adaptation policy, the degree of institutionalization varies considerably. EU cities operate within an established multilevel governance system supported by European policy instruments, whereas Russian cities follow nationally prescribed methodologies within a more centralized administrative structure. The results demonstrate that adaptation to climate change has become a central driver of transboundary cooperation and a defining dimension of urban international engagement in the Baltic region. A typological convergence of adaptation strategies is observed, driven by the influence of supranational institutions and the embedding of cities in transnational networks. This convergence reveals a persistent tension between locally grounded priorities and the imperative for coordinated action at regional and global levels. The study concludes that effective adaptation requires interconnected, multi-scalar collaboration among cities and regions, positioning transboundary cooperation not only as a platform for knowledge exchange but also as a structural condition for achieving urban climate resilience.