Cystic fibrosis (CF) is a single-gene disorder with insufficient treatment options and a target organ, the lung that is relatively easily accessible. Thus, it is not surprising that in the early years of gene therapy, CF was at the forefront of this field. Since cloning of the CF gene in 1989, 25 Phase I/II clinical trials involving approximately 420 CF patients have been carried out using a variety of viral and nonviral gene transfer agents. Most early trials focused on the nasal epithelium as a surrogate for the lung to allow for easy access and sampling, and, importantly, to ensure safety. Once an acceptable safety profile had been established, gene transfer agents were administered directly into the lung. Although many of these trials established proof-of-principle for gene transfer in the airways, a gene therapy-based treatment has not yet been developed. Here, we will summarize the key findings of these clinical studies and describe current preclinical and clinical research aimed at further developing gene therapy for CF.