Development Media International (DMI) creates evidence-based behaviour change campaigns to improve health and save lives. We deliver at scale to maximise impact and cost-effectiveness. We are the first organisation to scientifically demonstrate that mass media can increase life-saving behaviours. In 2018 DMI published the results of its 5-year, £7m randomised controlled trial (RCT) in West Africa which showed that 56% more children were taken for treatment for malaria, 73% more for diarrhoea and 39% more for pneumonia following exposure to our campaign. Modelling indicates that over 3000 lives were saved during the campaign and that our approach is one of the most cost-effective ways of saving children’s lives. We have subsequently undertaken a second RCT which showed that the modern contraceptive prevalence rate was 20% higher in areas exposed to DMI’s messaging compared to areas that were not.