Why do people behave in the way they do and how can we get them to change?  Drawing on a large body of empirical research, Lahlou shows that people’s behaviour is predictable and shaped by ‘installations’ combining three sets of factors: what is technically possible (affordances of the environment), what people are able to do (embodied competences), and what monitors and controls behaviour (social regulation).These channel our behaviour and incline us to act one way or another in specific circumstances – in the way, for example, that when you travel by plane, the steps you take from the moment you check in to the moment you take your seat are fixed and predictable. Lahlou shows how we can intervene at each of the three levels of installations to change human behaviour, and how we can combine them for greater effectiveness and direction, with a robust, step-by-step method.Because the method is so powerful, Lahlou also provides ethical guidelines and caveats about using these interventio