In this chapter, we report from a 4-year study of the systematic work at an organizational level towards a whole school approach to sustainability. Aiming to extend the individual good practices on Education for Sustainable Development (ESD) to include all schools in the municipality, a process of school development began in 2019, and was studied for 4 years until 2022. Through a narrative approach, we describe the process and its critical events. Different dimensions of the school improvement model devised by Scherp and Scherp are also identified and analysed. The results show that a cyclic process, including not only different actions but also reflections, is important for improvement and, furthermore, that the holistic idea is an important dimension that should guide structures as well as teachers’ professional development towards more successful work with ESD in a whole-school organization.