The Teacher Development Multi-Year Studies were initiated by the Australian Government’s Department of Foreign Affairs and Trade (DFAT) to provide evidence about the impact of DFAT’s investments in teacher development and how teacher development investments can be more effective. This Multi-Country Report is the culmination of five years of research across three countries, Timor-Leste, Vanuatu and Lao PDR (Laos), involving in-depth interviews, observations and learning assessments. Teacher development is at the heart of many education systems’ policies and programs aiming to improve teaching and student learning. The Multi-Country Report highlights how teacher professional learning can work together with system and contextual factors to lead to better outcomes. It provides a set of strategies for future thinking related to teacher development investments, and highlights how these investments need to be underpinned with sustained investment and robust systems to capture evidence of quality and impact.