Teachers in most American schools work in isolation, separated from other teachers, making it difficult to benefit from their colleagues' expertise or to share their expertise with others about how to help more students learn. However, a growing body of research shows that when teachers work more collaboratively, student outcomes can improve, teachers can be more satisfied in their jobs and teacher turnover can decrease. This research guide synthesizes research on teacher collaboration. Its goal is to help teachers, principals, superintendents and school board members reflect upon whether and how creating conditions for teachers to work more collaboratively might benefit students and teachers in their schools and districts.