The task of determining the structure of membrane proteins has been hindered by experimental difficulties. Recent success in crystallising a number of channels (K⁺ channel, Cl^- channel, Aquaporin 1 etc) and pumps (Ca²⁺ pumps) has led to the determination of 3D structures of a number of proteins responsible for selective transport of polar molecules and ions across biological membranes.In recent years several lines of evidence indicate that the lipids in the plasma membrane of animal cells are inhomogeneously distributed. Lipid rafts and caveolae are cholesterol-sphingolipid enriched microdomains. The characteristics of these domains, such as size, composition and dynamics were briefly reviewed in the present paper. A large number of signalling molecules are concentrated within these lipid microdomains, which has been proposed to function as signaling centers. Besides, the roles of lipid rafts in membrane transport were also discussed.