Purpose: The purpose of this paper is to outline how collective capacity building is supporting system-wide reform in one country. It seeks to outline the way in which professional learning communities within, between and across schools are creating an infrastructure for improving professional practice and raising standards. Design/methodology/approach: The paper is both descriptive and analytical. It draws on the international literature pertaining to system-wide reform and the empirical evidence concerning professional learning. Findings: The paper highlights some of the challenges in building the collective capacity for change throughout an entire system and reflects on progress to date. The paper concludes by arguing that despite the compelling case for collective capacity building, the real test is to make it happen. Research limitations/implications: The professional learning communities (PLC) programme in Wales is gathering evidence about impact but as the programme is just completing its first year of implementation these findings are not yet available. Originality/value: This paper adds to prior analyses and discussion of collective capacity building by providing a system-wide perspective. (Contains 5 notes.)