Cystic fibrosis (CF) is the commonest lethal inherited disease of white races, but it should be noted that in multi-racial Europe, no ethnic group is exempt from the disease, although prevalence varies across the continent. It is usually caused by the absence, dysfunction or reduced numbers of the multifunctional CF transmembrane regulator (CFTR) protein. Mature CFTR is produced after complex post-transcriptional and post-translational processing, which has implications both for prognosis and modern, genotype-specific, therapy. The protein has a key function in regulating the amount of water in the airway surface liquid. If the CFTR protein is not working normally, clearance of bacteria and particles from the lungs is impaired. Either correcting the dysfunction of this protein or dealing with the downstream consequences is key to developing therapies that will modify the natural history of CF.