Artificial self-assembling systems are currently widely investigated as an alternative approach to recombinant viruses for gene transfection in vitro and in vivo. Cationic lipids are particularly attractive, as a great variety of well-characterized reagents can be synthesized from there. Over the last few years, numerous cationic lipid systems have been developed and shown to be efficient for in vitro transfection. However, although some promising results have been reported in the in vivo setting (even in clinical gene therapy trials in man), the in vivo use of cationic lipid-based systems is still problematic, especially when considering the systemic route of administration. Herein, we summarize our own research on a particular class of cationic lipids, cholesterol derivatives characterized by polar headgroups with guanidinium functions, in order to illustrate the basic principles of and the positive results already obtained by cationic lipid-mediated gene delivery as well as the remaining problems that need to be urgently resolved, particularly as regards the systemic administration. In this forward-looking review, we also discuss the present efforts to develop modular systems for improved in vivo transfection. Indeed, lipidbased vectors offer the possibility to create sophisticated modular gene delivery systems capable of self-assembly via hydrophobic interaction between their components, the role of the different functional elements being to help in overcoming the distinct extracellular and cellular barriers to in vivo gene transfection into the various somatic target tissues.