If sustainability transitions research is to be relevant for upscaled diffusion of radical innovations and wide systemic socio-technical changes, then markets remain critical to account for. Founding frameworks in transition studies regard markets and market formation as important. Yet, the conceptualization of markets has so far not been elaborate: markets are mostly pictured as target areas for sustainable innovation and emphasis is on diffusion and user involvement. This special issue aims to unpack the notion of markets and market formation in sustainability transitions. The special issue contains in total 13 papers, which draw on theory from various scientific disciplines, use diverse research approaches, and cover a multitude of contexts. Altogether, the collection of papers stimulates broader theorizing of markets in sustainability transitions and the formulation of an agenda for future studies on markets in sustainability transitions. This editorial paper proposes relevant topics for such a research agenda. © 2022 The Author(s)