Design is all about behavior. We can help people make better decisions by designing (digital) products and services that stimulate positive and healthy behaviour. This will only succeed with a design that is fun and easy to use. To achieve this we use a user-centered approach. Interaction designers play an important part in this. When designing for behaviour change we combine our knowledge of design with our knowledge of psychology and substantiate this with field research. We aim to explore what people think and do, but also why they do what they do.