Gene therapy is a treatment procedure, where faulty gene in the cell that is responsible for causing disease is replaced with new functional genes or faulty gene is corrected. Gene therapy is useful to treat the disease or improve body's immunity to fight disease. Gene therapy hold promising role for treating some of chronic diseases such as AIDS, cancer, diabetes etc. Some techniques used in gene therapy are Gene augmentation therapy, Gene inhibition therapy, Killing of specific cells. Currently gene therapy holds its own challenges with future prospective to improve. This book discusses applications and recent advancements in the field of gene therapy.