The literature on outcomes and effectiveness of peer recovery support services in mental health and substance use disorder systems is nascent but growing. There is a greater body of research about peers in the field of mental health than in substance use. Generally, there is a lack of uniformity in the definitions of peers in the literature (O'Hagan, Cyr, McKee & Priest, 2010). There is also high variability and ambiguity about the roles that peers play and the scope of services they provide (Rogers, Kash-MacDonald & Brucker, 2009). Furthermore, measuring recovery tends to include such a wide variety of outcomes (e.g., symptom abstinence, sense of well-being, quality of life, social engagement, evidence of employment or enrollment in education, level of justice-system involvement, etc.) that there is lack of consensus among recovery scholars, administrators, and practitioners about what outcomes are the most salient to measuring both recovery and the efficacy of peers in supporting recovery efforts (Blash, Chan & Chapman, 2015). Despite the variance in definition and conceptualization, research supports the efficacy of peers across roles, settings, and implementations. This review aims to take the next step of identifying a cohesive and appropriate set of recovery outcomes that will broaden and solidify the promising base of literature. This literature review begins by situating the peer role into the context of recovery from mental health and substance use disorders by briefly describing the history of the advancement of peers in recovery fields. This context is followed by a more in-depth look at (1) how peers are defined by the literature, (2) the specifics of their role and fundamentals underlying their practice, and (3) considerations regarding the standardization of peers. The review then outlines common recovery outcomes typically measured for consumers with mental health or substance use disorders who receive peer recovery support services. The outcomes reviewed were categorized into two overarching domains. The review also briefly describes considerations for families and peers who deliver services, and stigma regarding disorders. Finally, recommendations of instruments used to measure recovery outcomes are provided.