As its major contribution to the United Nations Decade of Education for Sustainable Development (UN DESD, 2005-2014), the United Nations University (UNU) has promoted the establishment of Regional Centres of Expertise on education for sustainable development (RCEs) and their net-working to build innovative multistakeholder platforms for ESD locally and globally. In the first half of the UN DESD, UNU acknowledged 74 RCEs around the world. As an introduction to the special section on RCEs, this article highlights diverse roles that RCEs have taken and presents issues and challenges they have faced. It discusses RCEs as an engine for mobilising diverse stakeholders for ESD, a coordinator and an intermediary support structure for local-regional ESD activities and related initiatives in the region, and a facilitator of "social learning". (Contains 1 note.)