Co-teaching is an instructional teaching model that provides an opportunity for students to receive instruction in the least restrictive environment. An extensive literature review was completed in order to identify best practices and effective co-teaching practices in mathematics classrooms. A clearly defined purpose for co-teaching and selecting co-teaching partners is a key to the success of co-teaching. Also, student and teacher perceptions impact the implementation of co-teaching. The effectiveness of co-teaching is further impacted by co-teaching practices, along with the use of effective mathematical teaching strategies. The balance of maintaining effective co-teaching practices and mathematical teaching strategies is integral to the success of co-teaching. The literature revealed a lack of a consistent definition of what effective co-teachers are. Also, there is generally a lack of focus on student outcomes in co-teaching research. Finally, there is minimal research on co-teaching in mathematics.