“Social impact bonds, a recent innovation in social finance, are designed to harness capital and knowledge from private nonprofit, for‐profit, and public entities to address pressing social problems. Although there is great policy interest in understanding how social impact bonds can be used to tackle social problems, the emergent nature of social impact bonds makes it hard to find relevant data and evidence. To overcome this challenge, we use single‐significant‐case sampling as our research design strategy. We conduct an in‐depth case study of the Social Innovation Financing Youth Recidivism Project in Massachusetts. Our case study is comprised of a qualitative analysis of the multiparty contract and multiyear quantitative benefit-cost analysis to understand transaction costs. We draw upon contract theory to develop an analytical framework for the case analysis and highlight the risks and safeguards for the various parties to the contract, and conduct a formal benefit-cost analysis to map out transaction costs. We conclude with a discussion of study implications and future research.”