Abstract
Thermodynamics of liposome systems and their spontaneous vesicula-tion are briefly introduced. The importance of the system size on the stable structure is emphasized. Several examples of spontaneous vesiculation due to soft lipid bilayers (entropic stabilization) and asymmetric bilayers (enthalpic stabilization) are discussed. The use of the term critical micelle (or bilayer) concentration in the case of lipids with very low aqueous solubility is questioned.