 The article provides guidance for researchers on actions to take during intervention development. Key principles include seeing intervention development as a dynamic iterative process involving stakeholders reviewing published research evidence, drawing on existing theories, articulating program theory, undertaking primary data collection, understanding context, paying attention to future implementation in the real world and designing and refining an intervention using iterative cycles of development with stakeholder input throughout. Researchers should consider each action by addressing its relevance to a specific intervention in a specific context, both at the start and throughout the development process. This article was authored by Romana Newlands, Heather Cassie, Ailey M Duncan and others.