Gene therapy is the gene transfer into host cells for treatment of acquired and genetic disorders. For this purpose, there are a wide variety of gene delivery methods with special properties including viral and non-viral vectors. The non-viral methods use physical forces or chemical compounds (natural or synthetic) to transfer DNA into a cell. The efficiency of the non-viral gene therapy depends on conquering four different intra-and extra-cellular barriers such as cellular uptake, endosomal escape, nuclear entry, and gene expression. Among various gene carriers, some viral vectors such as Adenovirus, Lentivirus, Vaccinia as well as gene gun and lipofection achieved to clinical trials. In this mini-review, we briefly describe different approaches for gene delivery and their applications in various phases of clinical trials.