Cystic fibrosis is a common severe autosomal recessive genetic disease which is caused by dysfunction of an epithelial cell surface cAMP activated Cl- channel. The effects of this dysfunction are pleoitropic but the human morbidity results from the effects in the respiratory epithelium. Gene therapy is an attractive possible treatment, the gene required is well characterised and only low-level expression is required. The cellular target is accessible and the clinical effects of treatment should be readily assayable. This chapter reviews current proposals for suitable gene delivery mechanisms and vectors and discusses the clinical trials, the results from the first of which are now becoming available.