The discipline of global mental health has been singularly associated with the generation of knowledge which seeks to reduce the treatment gap for mental disorders. Its priority research agenda has focused on delivery science, i.e. the science of implementing evidence-based interventions. Considerable new resources have furthered this agenda, leading to a flowering of innovations to address barriers to the delivery of interventions while also contributing to the growth and consolidation of research capacity in low and middle income countries. A significant, but as yet under-recognised, opportunity of this global mental health initiative is its potential contribution to discovery science, notably research aimed at identifying the aetiology of mental disorders and the development of novel interventions. This editorial considers a range of potential themes for such discovery science and its guiding principles. Given the limited knowledge that we currently possess about the nature of mental disorders or their effective prevention and treatment, this may well be the most important ultimate contribution of global mental health, i.e. generating knowledge which not only reduces the treatment gap but the actual global burden of mental disorders, and will finally do justice to the 'global' of this discipline.