In this paper the current opinions on the structure and function of the lipid rafts heterogeneous, sterols and sphingolipids rich microdomains that occur in the plasma membrane but also in the membranes of some intracellular organelles e.g. Golgi complex, endoplasmic reticulum or mitochondria were presented. Lipid rafts have different dimensions. Their diameters often range from 50 to 100 nm, but larger forms with diameters of 200500 nm also exist. The smallest lipid raft with diameter of 5 nm lipid raft contains approximately 3040 lipids and 610 characteristic proteins. In spite of the small size of a single raft, the overall surface area of all lipid rafts accounts for approximately 30% of the entire surface of the plasma membrane. Depending of contents (mainly cholesterol) and protein-protein and protein-lipid interactions small rafts may coalesce to form structures 500 nm in diameter. Initially, lipid rafts were regarded as stable structures, that undergo only slow and slight temporal changes. As follows from the most recent experiments, these structures have been found to be highly dynamic, that constantly change their composition and play an important role in various biological processes. Moreover, it has been demonstrated that the same molecules occurring in the microdomains have different functions depending on which side of the plasma membrane (external or internal (cytoplasmic)) they appear. They may also translocate from one side to the other. The change of a position within the cytoplasmic and external sides of membrane depends on the amount of cholesterol and other lipids in the rafts, while the change of composition may take nanoseconds only. Lipid rafts were found to participate many cellular processes such as signal transduction, clathrin-independent (caveolar) endocytosis and others.