The development of theory- and evidence-based health education interventions is a complex process in which interventionists in collaboration with priority groups and stakeholders make many decisions about objectives, change techniques, intervention materials and activities, delivery modes and implementation issues. In this development process, interventionists have to find a balance between employing change techniques that should be effective in an ideal world, and intervention activities and materials that match the reality of priority populations and intervention contexts. Intervention descriptions providing information about what behaviour change techniques have been employed, do not reflect the complexity of this decision-making process. They do not reveal why interventionists have decided to include or exclude particular behaviour change techniques. They do not reveal that interventions are based not only upon considerations of health psychologists and other scientists, but also on practical and political boundaries and opportunities that set the scene for the effectiveness of change techniques. Intervention descriptions should therefore reveal not only what is included in the interventions, but also why the intervention is as it is. Intervention Mapping provides the tools that enable the production of such descriptions.