Inherited diseases, such a cystic fibrosis (CF), are caused by mutations in human DNA that are passed from mother and father to child. Gene therapy, which in its simplest form is the delivery of DNA to correct the effects of mutations, seems a simple approach to combat serious inherited diseases. Professor Stephen Hyde’s research group first demonstrated that the primary cause of CF could be tackled using gene therapy more than 25 years ago. The battle to convert that simple laboratory observation to a treatment that could improve the lives of patients with CF has been more complex than imagined. The path taken has revealed how humans natural defence mechanisms to infection hinders the development of genetic therapies and how viruses can be tamed to provide twenty first century medicines.