Informed by institutional entrepreneurship theory and based on the case of waste prevention projects in the City of Göteborg, this paper examines the role of cities in shaping new environmental policies. Structured by the research question, ‘How do cities shape novel environmental policies and practices?’, the paper illustrates how cities become agents of environmental change and institutional entrepreneurship through mobilizing and recombining resources (i.e. human, financial, and spatial), rationales (by reframing symbols, challenging taboos, and transforming waste socio-materialities), and relations (via internal and external collaboration and by creating new institutional arrangements, roles, and expectations). Emerging environmental policies, such as waste prevention, represent the structuring of an incipient environmental policy field. This new generation of environmental policies expands the scope of the public sector (the so-called publicness), reshapes the public/private distinction, and challenges taboos such as the intrusion of publicness into privateness.