Education for Sustainable Development and Global Citizenship (ESDGC) has received little detailed research attention, especially in Wales where it is now a key theme in the Revised Curriculum for Wales. The thesis explores issues in the development of ESDGC through case studies of five Welsh primary schools which had received positive mention for ESDGC. The schools’ practice is first examined against established criteria for ESDGC. A detailed investigation follows of the influences and dynamics that had shaped their development. All schools were found to be carrying out a substantial number of ESDGC activities and taking a flexible, pupil-centred, skills-based approach; this was further encouraged by the nature of the revised curriculum. One school displayed some characteristics of transformative change. ESDGC was found to widen pupils’ horizons and to give them enjoyment and motivation for learning. Although schools had begun developing ESDGC for varied reasons all had at some time been influenced by national guidance. Key factors in development included: having a supportive head teacher who gave attention to ESDGC; a knowledgeable, enthusiastic ESDGC coordinator; a collaborative ethos; being alert to, and taking advantage of, external opportunities to enrich learning. Key players had often received substantial professional development but other teachers were dependent on learning opportunities within the school. ESDGC coordinators had extensive external networks which gave them access to intellectual capital and new ideas. Where there were strong learning communities and frequent opportunities to discuss ESDGC there appeared to be greater understanding of ESDGC and a shared vision of its relevance. Several progressive models are proposed to explain the mechanisms of ESDGC development within schools and regionally. These draw on a combination of action research models, socio-historic activity theory and social network theory. Implications for national funding strategies, school networking, teacher training and educational change in general are noted.