Behaviour change interventions are deliberate actions, programmes or policies designed to influence the decisions and habits of individuals or groups. They can range from public health campaigns and workplace initiatives to digital apps and changes in law or policy. At their core, interventions aim to close the gap between what people intend to do and what they actually do. However, well-meaning initiatives do not always lead to meaningful change. Designing interventions that are evidence-based, drawing on behavioural science theory, empirical research and real-world evaluation, increases the likelihood that they will be effective.