This study by Brookings Institute provides:

Clear definitions of the concepts, key players, and development processes of impact bond transactions

A comprehensive inventory of all active 38 active SIBs (contracted as of March 1, 2015) as well as some of the social and development impact bonds in the development stage

An inventory of key policy actions and legislation to support the impact bond ecosystem An analysis of the stakeholder motivations, key facilitating factors, and biggest challenges faced in the 38 impact bond transactions

A critical examination of 10 positive claims made about impact bonds

An analysis of the future potential of impact bonds and any potential derivatives with a particular focus on developing country contexts