DNA internalization into cells is greatly improved if it is encapsulated in conventional liposomes or complexed with cationic liposomes. Although in the long-run encapsulation in neutral or anionic liposomes may be the more prospective approach, currently no data on these have been published and we shall mostly discuss the use of cationic liposomes. Conventional and sterically stabilized liposomes as a gene delivery system will be presented therefore in Chapters 11 and 13. In this chapter we shall discuss DNA–liposome and DNA–lipid complexes, from their preparation, characterization, scaleup, and quality control to their safety.