This document discusses social impact bonds (SIBs) and how they relate to public-private partnerships (PPPs) for infrastructure delivery. It notes that while interest in SIBs is growing, only a few are currently operating in the US. It argues that SIBs can help transfer performance risk from the public to private sector, address the "wrong pockets" problem by capturing value across agencies, help build an evidence base for innovative programs, and provide reliable funding for social service providers to scale up. However, it also notes that risk transfer through SIBs may increase costs and constrain future spending. Officials considering SIBs need to carefully analyze each project to ensure public value over traditional delivery. Lessons from PPP