"What Matters Most: Teaching for America's Future" by the National Commission on Teaching and America's Future tells that teacher quality is the single most important factor in determining student achievement, so principals are wise to put their efforts into improving teaching in their schools. However, principals do not need to take on that burden themselves, but rather they can share the work of improving instruction with every teacher in the school. Principals can do so by establishing professional learning communities (PLCs) in which teachers and administrators work toward the common goal of improving student achievement. In these communities, the most effective teachers not only get to share best practices with their colleagues, but they also have an opportunity to learn about other effective techniques to continue to improve their own teaching. Likewise, new teachers can learn from veteran teachers' wisdom of practice as well as contribute their own fresh perspectives. Veteran teachers and new teachers each have different skills and knowledge to bring to the table and share. PLCs improve the practice of all teachers in the school and ensure that students are being prepared to function in a 21st century economy. This article discusses the key components of PLCs. (Contains 3 online resources.)