Various order and disorder phenomena in lipid bilayers are considered as they arise due to the very many-particle character of the bilayer. Particular attention is paid to dynamically maintained order in terms of lateral density- and compositional fluctuations that lead to dynamic heterogeneity, local structure, and lipid-domain formation on length scales of 10-1000 Å. The influence of cholesterol and various drugs on the local structure is described. A discussion is presented of the possible role played by lipid order and disorder phenomena for the functional dynamics of membranes.