Book excerpt: In recent years, the term social innovation, or SI, has entered mainstream policy discourse; broadly construed, SI refers to pioneering, effective solutions to social problems that benefit society at large rather than individuals. This book explores the full meaning of SI and what it offers to people analyzing social policy, including the origins and background of the concept, the reasons for its rise to prominence, and the ways it has thus far been applied. Does it actually represent a significant departure in theory or practice, or is it merely a rhetorical change? Simone Baglioni and Stephen Sinclair offer here a rich analysis of the concept that will enable practitioners to reach informed conclusions.