The CGIAR Research Programs (CRPs) embodied a fundamental shift in the approach to research for development. In addition to producing highquality science, the CRPs explicitly assume shared responsibility for achieving economic and human development outcomes. This shift required new ways of working for positioning, prioritizing and planning of research, and better ways of monitoring and evaluating research. When the Forests, Trees and Agroforestry (FTA) program was established in 2011 it responded to the latter challenge by proposing to develop and use theory-based approaches for monitoring and evaluating outcomes and impacts. This concept was well received by reviewers at the time, and the approach has subsequently gained considerable traction in CGIAR as a whole. FTA’s Monitoring, Evaluation, Learning and Impact Assessment (MELIA) Program has actively adapted, developed, tested and refined a comprehensive set of concepts and methods, including using detailed, participatory theories of change; developing and refining actor-specific theory-based outcome evaluation methods; conducting a series of outcome evaluations of FTA research projects; systematically reviewing, defining and assessing the quality of research that crosses disciplinary boundaries (i.e. research for development); and developing, testing and refining a transdisciplinary research quality assessment framework. This work has generated valuable lessons about research design, implementation, monitoring and evaluation within FTA and beyond. Designing research in a way that allows intended contributions to be made explicit and testable increases the likelihood and the magnitude of positive outcomes and facilitates scaling. It also improves the ability to gather evidence, assess and communicate outcomes and impacts for enhanced accountability, and the capacity to learn from experience.