This document provides an overview of gene therapy. It discusses the definition of gene therapy as inserting genes into cells to treat disease. The history of gene therapy is described, including early research in the 1970s and the first human clinical trial in 1990 to treat ADA deficiency. The document outlines the main types of gene therapy as somatic, germline, and preventative. It also discusses gene delivery methods using viral and non-viral vectors and the advantages and disadvantages of gene therapy.