Teaching embodies many roles -- in the classroom through teacher-student interactions, and beyond the classroom through teacher-adult interactions. This book explains and demonstrates how collaboration and teamwork can help enhance professionalism and school quality by overcoming teachers' isolation in the classroom, in the school, and in their work. The contributing authors address: historic patterns of isolation; why collaboration is crucial for vibrant and sustained professionalism; principles of successful team collaboration in schools and other sectors; school districts' structure and support for collaborative teams; forces that motivate or restrain teachers' ability to collaborate; how teachers in grade-level teams perceive the quality of their training and support; team members' perceptions of their work in departments; teachers' use of evidence of student learning to improve teacher and organizational learning; and teacher-principal collaboration from the perspectives of exemplary teachers. These chapters provide insight into the complexity of teachers' roles, and indicate the necessity to build collaboration within the school and beyond.