This article outlines the progress and impact of professional learning communities within, between and across schools, as part of the implementation of whole system reform in Wales. It describes the way in which professional learning communities are being developed to support improvement and change across the education system in Wales. The article focuses on a group of schools that piloted a model of professional learning communities that subsequently have become a key part of the reform process in Wales and it highlights some of the challenges faced by the schools in establishing and sustaining professional learning communities. The article concludes by suggesting that professional learning communities offer one way of generating changed professional practice that can positively contribute to system-wide improvement. (Contains 2 notes.)