Co-teaching involves two professionals, often a special education teacher and a general education teacher, delivering instruction to students with and without disabilities in a single physical space. The popularity of co-teaching no doubt has been spurred by federal and state mandates promoting inclusive instruction and access to the general education curriculum for students with disabilities. This chapter examines the extant research base regarding the impact of co-teaching on student outcomes. It also examines research on co-teaching that has used other research designs (i.e., explanatory, quantitative descriptive, and qualitative) to more fully investigate the empirical support that exists for co-teaching. A number of co-teaching models have been described in the literature including: one teach, one assist; station teaching; parallel teaching; alternative teaching; and team teaching. The chapter concludes by discussing a theory-based explanation of research findings, challenges and issues to consider when examining the effectiveness of co-teaching, and the implications of research findings for policy and practice.