Gene therapy is used to treat genetic disorders, which may be achieved both ex vivo and in vivo. Gene-delivery systems usually include a carrier system which both protects the gene expression plasmid and allows its extracellular and intracellular trafficking. Viruses are used in most of the clinical trials today; however, they do have important drawbacks. Non-viral vectors based on lipids, water-soluble polycations, other non-condensing polymers and nano- or microparticles/capsules have been proposed. Cationic polymers. especially carrying novel targeting ligands. are receiving increasing attention. Intelligent polymers with temperature, pH, and light sensitivities for a controllable and effective non-viral transfection have recently been introduced but are just at the beginning. Our preliminary studies showed that block copolymers of N-isopropylacrylamide-acrylic acid with poly(ethylene imine) could be one example of these novel non-viral vectors.