For the past decade, behavioural science has been influencing public policy by applying principles of psychology, cognitive and social sciences, neuroscience and economics, to put individuals at the forefront of policy goals, and with an accurate rather than imagined understanding of human behaviour. Like any policy-making tool, the use of behavioural insights must be subject to ethical considerations that can arise at any point from scoping to policy scaling. This good practice guide offers practitioners and policy makers step-by-step guidance to prompt deliberations into how to use behavioural science ethically for public policy. It is designed to be a practical resource to promote the responsible use of behavioural science in the public sector.