 Gene therapy involves introducing foreign genetic material into host cells for therapeutic benefit, targeting diverse diseases with different inheritance patterns and acquired conditions. There are two main categories, germline and somatic gene therapy, but ethical restrictions limit the use of germline therapy. Various viral and non-viral delivery systems have been developed over the past 30 years, each with advantages and limitations for specific cell types in vitro and in vivo. This article was authored by Nori Nehrosadat, Thalebi Maide and Palisban Abbasali.