As new municipalism comes of age, prefixes proliferate: from democratic and autonomist to post-growth and care municipalisms. How do all these variegations relate to each other and to the wider movement of which they claim a part? What does all this conceptual creativity amount to, epistemologically and politically? How can we distill the most salient lessons for the further development of theory and practice in the years ahead? This article is our attempt to answer such questions and to define more precisely the contours of this emerging field of praxis. First, we delineate within new municipalism the target of our analytical gaze – radical municipalism. Radical municipalism is not simply progressive policies happening in cities, and should not be conflated with pragmatic, entrepreneurial or state-centric perspectives. Rather, we argue it is a speculative hypothesis about how systemic transformation might be wrought through coordinated action at the urban or municipal scale, understood as a strategic entry-point for counter-hegemonic struggle. Key here is proximity and the politicisation and socialisation of proximate relations of encounter and assembly. Second, we delve deeper into what we identify as four salient dimensions marking this terrain – economic reorganisation, democratisation of political decision-making, feminisation of politics, ecological transformation – as a multi-dimensional lens through which to introduce, and situate within the wider literature, the 15 articles that comprise this double special issue. Throughout these contributions to the theory and practice of municipalist strategy, the issue of crisis looms large: both historically, as an animating spur to action and opportunity for political intervention, and operationally, as a structuring condition and limiting factor of a strategy arguably in crisis itself. Finally, we reflect on the epistemological, methodological and political implications of pursuing radical municipalist strategies in the current conjuncture.