Due to new discoveries, gene therapy has gained a lot of popularity in recent years. Issues in the past which were troubling scientists and practitioners are now being easily resolved. The growth of secure and effective gene transfer and development in the field of cell therapy has now brought new ways to deal with varied diseases. The book aims at compiling information from different resources about various biological gene therapy tools, the important subjects covered are cancer gene therapy - biological concepts in the design of multifunctional non-viral delivery systems, gene therapy based on fragment C of tetanus toxin in ALS, lentiviral gene therapy vectors, transposons for non-viral gene transfer and retroviral genotoxicity.