This booklet synthesises the research on teacher professional learning and development that has been demonstrated to have a positive impact on valued student outcomes. Its findings relate to teachers who have received at least some initial teacher education and who are in the process of deepening their knowledge and refining their skills. The booklet should prove particularly useful to those who are involved in helping teachers develop the professional skills they need to teach challenging curricula to diverse students, including students who typically have not achieved well in some of the educational systems. Behind the ten key principles identified in this synthesis are four important understandings that arise from the evidence base: (1) Notwithstanding the influence of factors such as socio-economic status, home, and community, student learning is strongly influenced by what and how teachers teach; (2) Teaching is a complex activity; (3) It is important to set up conditions that are responsive to the ways in which teachers learn; and (4) Professional learning is strongly shaped by the context in which the teacher practises. Other booklets in this series elaborate on aspects of these key understandings. The focus of this particular booklet is on the interrelated conditions for professional learning and development that impact positively on valued student outcomes.