Many studies have found that supported employment (SE) has effectively helped people with severe mental illness obtain and maintain competitive employment. However, most SE studies have asked "What works?" rather than discerning what works for whom, in what circumstances, in what respects and how. It is important to understand the outcomes of SE and identify the impact factors (contexts and mechanisms) that can trigger them. Four literature databases were searched for studies that analyzed counseling settings. Overall, 104 publications met the inclusion criteria. The review showed that most of the research on SE programs were one-dimensional, looking at either the effects of SE programs, the client or the professional, or the relationship between clients and professionals. The model reveals that impact factors are interconnected and can have a cumulative impact on the client, professionals, and the environment.