Planned adaptation to climate change denotes actions undertaken to reduce the risks and capitalize on the opportunities associated with global climate change. This paper summarizes current thinking about planned adaptation. It starts with an explanation of key adaptation concepts, a description of the diversity of adaptation contexts, and a discussion of key prerequisites for effective adaptation. On the basis of this introduction, major approaches to climate impact and adaptation assessment and their evolution are reviewed. Finally, principles for adaptation assessment are derived from decision-analytical considerations and from the experience with past adaptation assessments.