This case study describes the process of conducting a specific type of systematic review and synthesis called realist review. A realist review is a type of systematic review used for synthesizing research on health and social interventions in which it is unclear how an intervention produces intended outcomes or not. The review identifies outcomes, which are the identified changes the intervention aims to achieve (positive or negative); mechanisms, which are the psychological or behavioral changes that that lead to outcomes; and the contextual factors (e.g., setting or clinician characteristics) that allow for mechanisms to be produced. These building blocks create context–mechanism–outcome configurations that make up the realist theory. For the present review, motivational interviewing for adolescent health behavior change is the chosen intervention of study. Previous research has indicated that motivational interviewing is an effective intervention for improving health behaviors in adolescents. However, there is a lack of understanding as to how motivational interviewing works, who it works best for, and under what circumstances it works best. To answer these questions, a realist review was performed using self-determination theory as the candidate theory to be tested, as it is the leading theory of explaining the efficacy of motivational interviewing. From the systematic review of the literature, three context–mechanism–outcome configurations were formed that describe how and why motivational interviewing works and for whom it works best. The present case study describes the process in which the realist review was performed including the systematic search, data extraction, and theory formation.