Glycosphingolipids (GSLs) and sphingomyelin in animal cells are clustered and organized as membrane microdomains closely associated with various signal transducer molecules such as cSrc, Src family kinases, small G-proteins (e.g., RhoA, Ras), and focal adhesion kinase. GSL clustering in such microdomains causes adhesion to complementary GSLs on the surface of counterpart cells or presented on plastic surfaces, through carbohydrate-to-carbohydrate interaction. GSL-dependent cell adhesion in microdomain causes activation of the signal transducers, leading to cell phenotypic changes. A retrospective of the development of this concept, and current status of our studies, are presented.