This publication is a sequel to the OECD 2015 report on Social Impact Investment (SII), Building the Evidence Base, bringing new evidence on the role of SII in financing sustainable development. It depicts the state of play of SII approaches globally, comparing regional trends, and assesses its prospects, with a special focus on data issues and recent policy developments. Importantly, it provides new guidance for policy makers in OECD and non-OECD countries, as well as providers of development co-operation, development financers, social impact investment practitioners and the private sector more broadly, to help them maximise the contribution of social impact investing to the 2030 Agenda. In particular, it provides four sets of recommendations on financing, innovation, data and policy for delivering on the “impact imperative” of financing sustainable development.