The aim of this article is to propose a new analytical framework for comparing and explaining the emergence and diffusion of European regional mountain initiatives (ERMIs), envisaged as ‘functional regulatory spaces' (FRS). The article examines three exploratory hypotheses. The first hypothesis considers that the different ERMIs (Alps, Pyrenees, Jura, Carpathian, Balkan Mountains, Dinaric Arc, Caucasus) can be compared, distinguished, and classified using the FRS approach. The second hypothesis addresses the relationship between the degree to which ERMIs correspond to an ideal-type FRS and their role and position within policy diffusion processes. We suggest that the more an ERMI corresponds to an ideal-type FRS, the more important is its role in diffusion processes. The third hypothesis focuses on the relationship between the degree of formalization and institutionalization of ERMIs and their role in policy diffusion processes. We argue that the more and the earlier an ERMI is ‘‘formalized'' and ‘‘institutionalized'' in a clear and robust way as a ‘‘mature'' FRS, the more important its role, and the more central its position, in diffusion processes. This article is a very first attempt to link FRS and policy diffusion concepts. As such it seeks to assess the link's feasibility and relevance, rather than a definitive empirical (in)validation of the three hypotheses.