Strategic environmental assessment (SEA) is one of the main tools available to achieve integration of the principles of sustainable development into country policies and programmes. This guidance explains the benefits of using SEA in development co-operation and sets out key steps for its application based on recent experiences. Twelve different entry points are identified for the practical application of SEA in development co-operation. For each entry point, the text provides a guidance note: a checklist of questions and hands-on case studies. Evaluation and capacity development for SEA processes are also addressed.