This paper is focused upon exploring the development of the green economy in particular locations, with the aim of identifying why some cities and regions have been successful in engendering green growth. To date we have little idea where the green economy is developing, nor much insight, beyond anecdotal evidence, into why certain cities and regions appear to be more successful than others in this regard. We position our analysis within the context of research on socio-technical transitions that has theorised the potential shift to a more sustainable economy. We review the literature on sustainability transitions and the development of the multi-level perspective encompassing niches, regimes and landscapes. However, most research into socio-technical transitions has not given adequate consideration to the influence of places and spatial scale in these transition processes, and we therefore critique the socio-technical transitions literature from a geographical perspective. In this paper we are interested in four key questions: what role does the enabling and facilitative state play in these cities and regions? What new institutional forms and governance structures are being developed? How do actors in particular cities and regions construct their green vision, and how do they encourage other actors to buy-in to this vision? How are links across levels and spatial scales developed to connect niches with the regime? We address these through a focus upon the Boston city region in the USA, drawing upon both primary and secondary research material. We utilize this case study example to re-examine and re-theorize work on sustainability transitions from a spatial perspective.