There is a resurgence of interest in mental models due to advances in our understanding of how they can be used to help design and due to the development of practical methods to elicit them. This book brings both areas together with a focus on reducing domestic energy consumption. The book focuses on how mental models can be applied in design to bring out behaviour change resulting in increased achievement of home heating goals (reduced waste and improved comfort). This book also offers a method to extract and apply mental models to interface design. The approach enables mental models to be applied across domains when behaviour change was sought, and is validated as a useful design method.