Since the discovery of liposomes or lipid vesicles derived from self-forming enclosed lipid bilayers upon hydration, liposome drug delivery systems have played a signiยฎcant role in formulation of potent drugs to improve therapeutics. Currently, most of these liposome formulations are designed to reduce toxicity and to some extent increase accumulation at the target site(s) in a number of clinical applications. The current pharmaceutical preparations of liposome-based therapeutics stem from our understanding of lipidยฑdrug interactions and liposome disposition mechanisms including the inhibition of rapid clearance of liposomes by controlling size, charge, and surface hydration. The insight gained from clinical use of liposome drug delivery systems can now be integrated to design liposomes targeted to tissues and cells with or without expression of target recognition molecules on liposome membranes. Enhanced safety and heightened efยฎcacy have been achieved for a wide range of drug classes, including antitumor agents, antivirals, antifungals, antimicrobials, vaccines, and gene therapeutics. Additional reยฎnements of biomembrane sensors and liposome delivery systems that are effective in the presence of other membrane-bound proteins in vivo may permit selective delivery of therapeutic compounds to selected intracellular target areas.