Social influence is one of the most cited and yet least understood concepts in strategy and public policy today. While many people understand its critical importance in viral marketing campaigns, technology adoption, protest movements and other collective behaviours, there is little agreement on how it can be measured and harnessed for the greater good. So what methods and tools do we have for quantifying social influence? How can we design peer-to-peer interventions that make the most of digital technologies and the structural properties of social networks? In this post I review this and explore how we can leverage the dynamics of social influence to engineer social change.