I have worked as a researcher in the field of energy systems analysis, and energy and climate policy analysis for more than 25 years. Starting out in the areas of systems analysis and technology assessment my research interests quickly grew into understanding mechanisms and instruments of change in energy systems. The topical focus has been on renewable energy and energy efficiency in the context of evolving energy systems. There is ample evidence that energy for sustainable development is viable from a resource, technical and economic perspective. Deep cuts in greenhouse gas emissions are necessary in the next 20-30 years in order to avoid dangerous climate change. A current research focus is decarbonisation of the energy intensive basic materials industry and associated policy strategies.