In recent years, public agencies have frequently deployed behavioural insights to generate benefits for society, through encouraging citizens to comply with official requests, and more generally encouraging them to cooperate with public agencies to help deliver outcomes of collective benefit. In parallel, there has been a large increase in the amount and quality of the research evidence available on behavioural public policy. This review takes two contrasting areas where behavioural insights have been used: tax collection where government policy is compulsory (i.e. requiring compliance), and energy use where social objectives are non-compulsory, and achieved more by persuasion and encouragement. Processes of modifying and changing behaviour require different approaches whether the change is deemed necessary by the state or not. In taxes, the sole use of enforcement is rarely efficacious, whereas increasing the uncertainty of follow-up and audit increases compliance. Offering discounts for energy bills appears to be an effective method for achieving cooperation. However, the use of social norms and increased information and professional advice is effective for both compulsory and non-compulsory areas of compliance and cooperation. This has important implications for policymakers, who may be seeking effective methods of encouraging behaviour change. While there are differences in approaches for compulsory and non-compulsory areas of policy, there may be areas that move from non-statutory to statutory in the future. In this case, the development of desired social norms appears to be the most effective method of ensuring overall compliance.