"Design roles are expanding in society, as reflected in a growth of interest and funding for design and design research in the area of ‘social innovation’. By social innovation here, I refer to the provision of social services and resources, such as habitation, education, care, mobility and food, in which design is increasingly engaged in the complexity and dynamics of local provision of such services and resources, and in the co-production of alternatives. The question of designing for social innovation necessarily involves political questions about the role of design in how, where, by and for whom, and in what forms, wider social practices and systems, beliefs and authority, may be altered. To explore such questions, I outline methodological approaches, emergent themes and key examples from three case studies, in the US, Denmark and The Netherlands, in which designers, design methods and materials took part in issues and controversies of sustainable development. In these cases, design had roles in (re)producing or rupturing a particular ‘commons’ in terms of how and where social innovation is framed and staged, for and by ‘who’ and in ‘what’ forms.