This Research & Policy Brief addresses the aspect of the teacher support system that is perhaps the most important and often the most weakly implemented: teacher learning and development. This brief includes the following to help state and district leaders select professional learning activities that are worth the allocation of scarce resources: (1) A summary of current research and policy related to high-quality professional development; (2) A discussion of factors that decision makers need to consider when making resource allocation decisions; (3) A description of evaluation methods for professional learning activities; and (4) Examples of promising approaches to professional development. High-Quality Professional Learning Activities Self-Assessment Tools are appended. (Contains 1 figure and 3 tables.)