The involvement of private sector actors in low carbon urban transitions is a neglected element of geographical analysis. Drawing on Polanyian, cultural economic geographies and the non-capitalocentric ethics of JK Gibson-Graham’s diverse economies perspective, the paper engages with the wider literature on the engagement of small and medium enterprises (SMEs) in environmental action, corporate social responsibility and low carbon transitions to develop a substantivist account of the contribution of SMEs to local low carbon transitions. The paper argues that, contra formalist economic analyses of economic rationality, SME owners should not be thought of as uncritical profit maximizers but as actors in favour of positive low carbon futures. Thus the paper argues that Polanyian economic geographies and diverse economies perspectives, which rarely speak to each other, can be drawn together, and concludes with suggestions for future research.