In this brief, we offer policymakers and pay for success (PFS) stakeholders principles to help them understand and interpret evidence and lay the groundwork for incorporating evidence into broader public decisionmaking. We explore the following questions:

• What is evidence?
• Why does evidence matter for PFS projects?
• How do you assess the quality of existing evidence and program evaluations?
• What do you do when the evidence base is limited?

While we look retrospectively at the evidence base for social programs, two accompanying briefs look prospectively at selecting strong evaluation designs for a PFS project to determine payments and to continue building the evidence base for other programs.