Good basic education depends on several factors working in harmony. The first is that students be healthy, safe, and ready to learn. Other essentials include an enabling policy environment and transparent management; a curriculum that reflects the society's values and aspirations for learning; and community support for education and parents' involvement in the lives of schools (UNESCO 2004; UNICEF 2000). The most important element of all, according to much current research and program experience, is the quality of teachers (ADEA 2004; Anderson 2002; Boyle, While, and Boyle 2003; Lewin and Stuart 2003; USAID 2002). Over the last two decades, the Academy for Educational Development (AED) has worked extensively with programs that address all of these crucial areas of basic education. This paper focuses on AED's approaches that address the heart of education: strengthening the quality of teachers and teaching through ongoing professional development at the local level. This paper summarizes the context and rationale for evolving approaches to teacher professional development, describe AED's early programs in this context, and outline a basic framework of AED's flexible and dynamic approach to decentralized, school- and cluster-based teacher professional development programs. The final section consists of six case studies showing how the approach has been adapted to strengthen teacher skills, morale, and professional commitment in Guatemala, Nicaragua, Uganda, Ghana, Namibia, and Ethiopia.