This chapter describes the relation between membrane architecture and membrane function. Life in all its diversity became possible after nature had found the trick with the membrane. It enabled the separation of living entities from the lifeless and hostile environment under preservation of selective material exchange between the two worlds. It led to the evolution of cells the function of which depends on the well controlled interplay and material exchange among compartments performing different functions. Simultaneously, the biomembranes developed into sites of essential biochemical functions, such as protein biosynthesis or oxidative phosphorylation. The chapter discusses the basic principles of the molecular design of biomembranes and some of their fundamental functions are introduced. It is also an attempt to point out universal physical properties may play a role in biological functions. Examples are the entropy driven repulsion forces and their role for bioadhesion or the role of membrane bending energy for the stabilization of cell shapes or for shape transitions.