In order to do justice to the richness and complexity of the ESD concept and ESD practices, this publication is divided into two parts: Understanding Education for Sustainable Development and Implementing Education for Sustainable Development. The first part provides an overview of how the concept of ESD has evolved over the years with a focus on the key competencies and thematic areas. The second part explores how ESD is implemented in the five Priority Action Areas of the GAP and how efforts are being scaled-up and monitored in the context of the 2030 Sustainable Development Agenda.