Glycolipids (glycosphingolipids) are involved in various biological phenomena by regulating cell-cell interactions and membrane receptor signal transduction. The physiological functions of individual glycolipids have been elucidated through phenotypic analyses of knockout (KO) mice lacking genes involved in their biosynthesis. In recent years, the use of double KO and conditional KO mice has further advanced the functional characterization of these molecules. Most of the major KO mouse lines have been deposited in public bioresource centers.