Who are behavioural public policy experts and how are they organised globally?

Behavioural public policy has spread internationally over recent years. Worldwide, expert units are translating insights from behavioural sciences into policy interventions. Yet, behavioural expert networks are a puzzling case. They seem to oscillate between two modes of collective action: as an epistemic community, they are based on the consensual belief that biases in behaviour pose a problem for policymaking. As an instrument constituency, they bring together a diversity of actors, unified not by consensual beliefs about problems but by practices of promoting behavioural instruments as solutions. Drawing on a review of literature, this article provides a systematic analysis of the relation between epistemic communities and instrument constituencies. It argues that there has been an `agency shift' from one mode to the other. The implications are that experts should be aware of the fact that the instruments they are proposing might develop a political life of their own.