On the micrometer scale, the behavior of membranes and vesicles can be understood, to a large extent, in terms of a few parameters. Two of these parameters, which are crucial for the membrane morphology, are the vesicle volume and the preferred or ‘spontaneous’ curvature of the membrane.1 The volume is primarily determined by the osmotic conditions, i.e., by the concentration of solutes such as ions, molecules, and colloids which are dispersed in the aqueous solution and which cannot permeate the membrane. These particles can also be used to change the ‘spontaneous’ curvature in a systematic and controlled fashion. Another local control mechanism for this curvature is provided by molecules which are attached to the membranes via hydrophobic anchors. These control mechanisms might be used in order to construct membrane machines such as swimming vesicles which are based on cycles in shape space.