Spatial planning defines how men use one of the most important and scarce resources on Earth: land. Planners therefore play a key role in countering or deepening the current ecological crisis. To foster ecological transitions, planning scholars and practitioners need to be equipped with sound theories and practical tools. To this end, this book advocates a re-foundation of spatial planning under the paradigm of “ecological rationality”, based on the revaluation of early pioneers of ecological planning and mutual fertilization with different disciplines, including decision-making science, ecology, (eco)system theory, land use science and political ecology.The key principles of ecological rationality and its application to spatial planning are discussed and this conceptual framework is used to explain the main underlying drivers of ecological degradation and their spatial manifestations at the local level. Current policy instruments in the European context, which can be used to underpin ecological planning, such as Green Infrastructure and the Mapping and Assessment of Ecosystem Service (MAES) initiative, are also examined.