Abstract Lipid microdomains, referred to as membrane microdomains, membrane rafts, or lipid rafts, are the highly dynamic nanoscale liquid-ordered, sphingolipid-, and sterol-rich domains in the plasma membrane. Lipid microdomains recruit specific proteins and form sophisticated lipid–protein assemblies as the result of lipid–lipid, lipid–protein, and protein–protein interactions that are involved in many cellular processes, including signaling pathways, endocytosis, and protein sorting. Moreover, lipid microdomains play a role in pathogenesis of various diseases. Resistance of cold nonionic detergent Triton X-100 to solubilization is used as a common tool to study lipid rafts structure; however, detergent-based artifacts were observed. Despite a vast amount of experimental work in which the noninvasive, detergent-free methods were used, the facts concerning the structure and functions of lipids microdomains in living cells are still disputable. This chapter consists of selected topics on current knowledge on membrane microdomains enriched with controversial data, and it presents variety of factors responsible for the impressive dynamic of plasma membrane planar organization.