PurposeThis study investigates barriers to social impact bond (SIB) implementation through a review of academic and gray literature. A SIB is a type of public policy instrument that leverages payment for performance (P4P), contracting together with private investments in the delivery of welfare programs. Outcome-based contracts, such as SIBs, are gaining attraction for public service providers in developed countries, but research regarding their implementation remains underexplored both empirically and theoretically.Design/methodology/approachA literature review is conducted in which two types of documents are included: (1) empirical research papers and (2) evaluations of completed SIB projects. In total, 43 documents have been investigated. The study engages in a comparative design where insights across sectors (healthcare, social care and employment/education), are leveraged. The insights rest on evidence from the UK and US.FindingsThe investigation reveals five types of barriers to SIB implementation related to: (1) the SIB model, (2) organizational competencies, (3) data infrastructure, (4) stakeholder engagement and (5) the institutional context. The study discusses ways of managing these barriers and develops a conceptual framework for empirically investigating SIB implementation.Originality/valueThis study is the first academic paper to systematically assess insights regarding the implementation of SIBs. Also, the article proposes a conceptual framework for investigating SIB implementation.