Transboundary mountain regions in Europe emerge as normative spaces at the intersection of territorial and environmental governance. Constituting a meeting point of different national legal orders under the umbrella of international regimes, they have become natural laboratories for the development of cross-border law. The objective of this article is to examine the nature and normative dimension of such legal environments. To this end, we introduce the concept of ‘melting law' as a means to assess the re-combination of different modes of conventional, national, international, supranational and/or interregional normativities. Hard (national) laws melt within the framework of transboundary mountain regions as a legal category, based on a mixture of national, international (or EU) and interregional norms, each combining with the other by softening their usual normative impact. Building on a review of legal approaches to mountains and cross-border cooperation practices, we trace the development of ‘‘melting law'' and ‘‘melted law'' through a discussion of the legal framework for and the impact of ‘‘working communities'' and the ‘‘European Grouping for Territorial Cooperation'' (EGTC). The discussion mobilizes a global approach with a view to generate new insights into the legal challenges facing transboundary mountain governance in Europe.