Direct gene transfer for the treatment of human diseases requires a vector which can be administered efficiently, safely and repeatedly. Cationic liposomes represent one of the few examples that can meet these requirements. Currently, there are more than a dozen cationic liposome formulations. These liposomes bind and condense DNA spontaneously to form complexes with high affinity to cell membranes. Endocytosis of the complexes followed by disruption of the endosomal membrane appears to be the major mechanism of gene delivery. The effectiveness and safety of this DNA delivery method has been established in many studies. Two human gene therapy clinical trials using cationic liposomes have been conducted and more trials will be started in the near future. In the field of gene therapy, cationic liposome is struggling to meet expectations.