Behavioural policy solutions pose challenges for politics, the law and science. These very broad charges will be sustained through a series of sketched arguments that criticize the intellectual foundation, political implementation, and democratic compatibility of the behaviour change agenda. These arguments take the form of what we call an institutionalist perspective on behaviour change, which attempts to defend the societal value of the areas under investigation. First, behavioural change instruments undermine the normative function of the law. Second, behaviour change, as a technocratic project, removes normativity from the political sphere by circumventing public deliberation. Third, behaviour change, as a movement that aims to bring science to policy, relies on a simplistic view of science which might jeopardize both: science and policy. We propose remedies for each of the difficulties and tensions we diagnose.