In recent years, social innovation has been increasingly practiced by individuals and their communities, as well as the civil, public and private sector. Although it has practically existed for two hundred years now,1 the pressing social, economic and environmental challenges that cities have recently come to face, together with proliferating advancements in Information and Communications Technology (ICT) have brought social innovation to the forefront of urban development practice and policy. Social innovations are literally everywhere. They happen across and in-between sectors (public, private, civil), they span an extremely large variety of areas (economy, environment, social inclusion, integrated development and others), and they transform urban life in unexpected ways. Social innovations are widely understood as new ideas that aim at meeting social goals (Manzini, 2014; Mulgan, 2006a, 2006b). They are so widespread and game-changing nowadays, that it is impossible to ignore them. The ‘smartest’ and most innovative governments and policy making authorities capitalize on this old but renovated concept by incorporating it in public policy agendas and providing funding, training and networking opportunities for social innovators and their communities. Social innovation has a central role in the European Union (EU)’s Europe2020 strategy towards smart, sustainable and inclusive growth,2 which includes the flagship initiative ‘Innovation Union’, whereby innovation is regarded not as merely industrial, but rather as a means to actualize society’s capacity to organize, act and respond on the persisting challenges of growth, and capitalize on the knowledge generation and transfer opportunities provided by new technology. The European Commission (EC) has in operation a host of different policy instruments to foster social innovation, ranging from networking platforms to financing tools for social innovation initiatives (European Commission − Directorate-General for Internal Market, 2016). Next to the institutional interest on social innovation, leading researchers on sustainability have underlined its importance in contemporary societies due to the new and extraordinary possibilities it opens (Bawens, 2007; Manzini, 2014; Murray, 2009; Tapscott and Williams, 2007). Nevertheless, the all-encompassing idea of social innovation has created conceptual ambiguity as to what it means and how it is practiced. Recent literature calls for more sector-specific research, in order to reach more detailed understanding of its content and particular characteristics (Grimm, Fox, Baines, & Albertson, 2013; Bureau of European Policy Advisers, 2011). Addressing this research gap, in this paper we focus on social innovation for sustainable urban development.