This chapter offers a survey of the latest concepts and thinking around social innovation developed by a selection of leading opinion-makers from academic centres and social innovation hubs around the world. It presents five chosen variables: impact and degree of social transformation, cross-sector collaboration, economic sustainability and long-term viability, innovation type, and scalability and replicability. There is an increasing demand to measure social impact and the degree of social transformation from a range of stakeholders, particularly funders, investors and governments, as well as social entrepreneurs themselves. The relationships between universities, industry and government are another set of cross-sector collaboration that has attracted attention as universities are playing an increasingly important role in innovation in knowledge-based societies. The chapter explores the complex relationship between social innovation and economic sustainability. Although social innovation builds on a great deal of robust research around innovation in the fields of medicine, technology and business, it is still an immature science.