Gene therapy is a medical/surgical intervention currently being developed, in which genes are introduced into cells in order to treat or cure a wide variety of human diseases, The field has evolved over the past four decades, with most experimental gene-therapy studies based on the use of viruses to deliver the genes of therapeutic interest, More recently, a large number of non-viral approaches to gene therapy have emerged, yielding promising pre-clinical results, and which are currently being evaluated in early stage clinical trials.