The property of all biological membranes is that they are curved. The state of many membrane proteins, both bound and integral, depends on the curvature of their location, while they can also influence this curvature. This interplay will be illustrated by two examples. The mechanism by which an amphitropic protein, Apolipoprotein H, causes vesicle budding will be described.1 Parameters determining vesicle shape will be defined and the structural features of this protein that are responsible for their modification will be indicated. Experimental verification of this model will be demonstrated. In the second example, the recently observed2 effects of vesicle shape on the lateral distribution of potassium channel KvAP will be explained by curvature mismatch between the intrinsic curvatures of that part of the protein embedded in the hydrophobic interior of the bilayer and the principal curvatures of the surrounding bilayer. This example also provides a test of the theoretical prediction3 that proteins accumulate preferentially at those membrane sections where the interaction energy between the protein and its lipid environment is smallest and that vesicle shapes change in the direction of increasing the sizes of these sections. In conclusion, we promote the view that vesicle shape behavior forms the basis of many cellular processes and that membrane proteins have evolved so as to modify this behavior to make these processes more efficient. The implications of this view will be substantiated by interpreting the function of the membrane skeleton of red blood cells and by the concept of the mechanical basis of cellular polarity.4