Procuring a service provider and implementing an intervention in a pay for success (PFS) project require a greater focus on outcomes, performance management, leadership, and organizational strength than in a business-as-usual project. This report describes key elements of program implementation in early childhood education (ECE) PFS projects. It is part of a larger toolkit for states, localities, and investors considering early childhood PFS projects. Its content is based in part on stakeholders' experiences with ongoing PFS projects. In the first part of this report, we outline the process for selecting a service provider in PFS, including the criteria that can identify service providers that would be a good fit for a PFS project. The second part of the paper discusses best practices for PFS project governance. In the final section, we discuss the iterative process in PFS projects for monitoring implementation and making course corrections, as well as the distinction between performance management in PFS projects and in the status quo, and the efficacy of pilot or ramp-up periods. (author abstract)