As reviewed gene therapy is a powerful tool for the prevention and cure of diseases as it aims to treat the cause rather than the symptoms of the diseases. Gene therapy is defined as the correction of dysfunctional or deleted genes by supplying the lacking component as a means to permanently treat or reverse diseases. There are a number of human diseases both genetic and acquired for which gene-based therapeutic approaches are gaining popularity. There are two types gene therapy which is germ line gene therapy and Somatic gene therapy. Two main approaches to gene therapy include in vivo and ex vivo. Ex vivo gene transfer techniques usually involve the genetic alterations of cells (cell lines or human cells), mostly by use of viral vectors, prior to implanting these into the tissues of the living body. In vivo gene therapy means direct introduction of genetic material into the human body. Applications of gene therapy would be narrow if one uses the term as a synonym for transfer of genetic material to specific target cells using carriers or delivery vehicles called vectors. Vectors are usually viral but several non-viral techniques are being used as well.