Gene therapy has become a revolution and its breakthrough is a corner stone in modern science. This treatment has rising advantages with limited negative aspects. Gene therapy is a therapeutic method in which, transfer of DNA to an individual to manipulate a defective gene is performed and to mitigate a disease which is not responding to pharmacological therapy. The gene therapy strategies are divided into two main categories such as direct in-vivo gene delivery of manipulated viral vector vehicle into the host and ex-vivo genetically engineered stem cells. In this review, we tried to cover all aspects of gene therapy studies; starting with the concept of gene, its treatment, gene delivery system and types, clinical trial either by vitro or In-Vivo -Clinical Trials and Clinical  ...