This teacher-friendly research synthesis describes professional collaboration among educators. It discusses the importance of collaboration, particularly for multilingual learners and highlights the shift from viewing multilingual learners as a separate group in need of remediation to viewing them as part of a larger continuum of English language development. It emphasizes the use of a cyclical process of collaboration, including co-planning, co-teaching, co-assessing, and co-reflecting to support the language and content development of multilingual learners. It describes a shift from an isolated, fragmented 20th century pull-out model to an inclusive and integrated 21st century in-class support model. It highlights the use of various tools and strategies to support collaboration. It emphasizes the importance of leadership in establishing a culture of collaboration.