The financial crisis has put pressure on governments throughout the world to reduce deficits with severe budgetary cuts in many welfare areas by reinforcing the need to modernize social policies and optimize their effectiveness and efficiency. Social impact bonds (SIBs) have rapidly become one of the most innovative financial schemes used by governments to privatize the upfront costs of welfare interventions by reducing taxpayer expenditure. Our analysis focuses on healthcare impact bonds (HIBs) that correspond to the adaptation of SIBs to health programs and are considered to be a viable way to fund out-of-pocket and preventive programs, especially considering the recent cuts to public healthcare expenditure. By using an in-depth qualitative analysis of existing practices based on a multiple case study approach, this study contributes to the ongoing debate on the role of SIBs for the future sustainability of welfare systems by proposing reflections and indications for the scalability and replicability of SIBs. With respect to the existing literature, this paper provides a theorization of the main scaling ingredients to be considered for the development of the SIB market as a supporting financial approach for new and emerging welfare needs by also proposing suggestions and insights and serving as a guide for scholars and practitioners.