This chapter shows that freeze-fracture electron micrographs of reconstituted, intrinsic, and induced membrane structures to underline the potential of liposomes as a model system to mimic membrane structures and to study membrane structure transformations. Biological membranes consist of a multitude of components which together carry out the diverse functions that characterize a particular membrane. All membrane structures described, whether they are reconstituted, intrinsic or induced, have been studied extensively by a multiplicity of techniques, among them freeze-fracture electron microscopy. Halophilic and thermophilic archaebacteria are growing under extreme conditions. Thermoplasma acidophilum cells are protected from the acidic and hot environment by a cytoplasmic membrane only, without an additional cell wall. Some of the vesicles are situated directly under the bulges of the nonplanar structured liposome membrane. Lipids isolated from biological membranes have long been known to form liquid crystalline phases when mixed with excess water.