Abstract Social Impact Bonds (SIBs) are a new mechanism for delivering public services. This article reviews the emerging SIB literature in high‐income settings. It identifies three distinct narratives: a public sector reform narrative; a financial sector reform narrative; and a cautionary narrative. These are analyzed relative to three themes: public versus private values; outcomes contracting; and risk allocation. The first two narratives are complementary and offer a ‘win‐win’ portrayal of SIBs. The third narrative challenges this dominant commentary by highlighting potential risks. There is limited empirical evidence on active SIBs to support these narratives. SIBs may have the potential to align public and private interests while improving outcomes for people affected by entrenched social problems, but this is yet to be established and appears less probable than the third more cautionary narrative. More empirical research is needed to consider the potential risks, drawbacks, benefits and alternatives of SIBs in different settings.