There is a great need for effective interventions to prevent or treat obesity. To be of use in a public health context, however, these interventions must be feasible and cost-effective on a large scale as well as in a controlled (and resource-intensive) experimental setting. It can also be challenging in general to conduct appropriate research for behavioural, psychological and environmental interventions. Explanatory trials and proof of concept studies represent an important gap in research. Across all these areas, a balance between studies on prevention and on treatment will be required to produce a balanced approach to obesity and its related diseases. The identification of critical points in the life course for intervention will be important, as will investigation of differences in effectiveness of interventions between different groups (eg age or cultural groups).