This issue features the final literature review in the Assessing the Evidence Base (AEB) Series. Sharon Reif, Ph.D., and colleagues found a moderate level of evidence for the effectiveness of peer recovery support for individuals with substance use disorders. Peer recovery support providers highlight their own lived experience and act as recovery catalysts to motivate and empower clients. They help clients acquire resources to restructure their lives and achieve and maintain recovery, often acting as liaisons with formal behavioral and general medical treatment services, housing and employment programs, and other systems. More broadly, peer providers serve as advocates for the individual and for the recovery community. Research has demonstrated reduced relapse rates, increased treatment retention, improved relationships with treatment providers, and increased satisfaction with the overall treatment experience. Dr. Reif and colleagues conclude by describing research needed to build a more robust evidence base for these services, which remain outside the traditional provider spectrum and are thus inconsistently reimbursed (page 853). The AEB Series, which is funded by the Substance Abuse and Mental Health Services Administration (SAMHSA), has provided updates of research on 13 commonly used interventions for people with serious mental illnesses. In a Taking Issue commentary, SAMHSA Administrator Pamela S. Hyde, J.D., and Miriam Delphin-Rittmon, Ph.D., an AEB Series author, underline the importance of implementing services with demonstrated effectiveness, as well as the need for innovation and ongoing research to improve outcomes for individuals, families, and communities (page 841).