Glycosylphosphatidylinositol (GPI) has diverse glycan structures depending on the species, organ, or cell [1] (Fig. 37.1). In eukaryotes, GPI plays a role in anchoring proteins to the cell membrane, with the glycan linking the protein to the phospholipid. By contrast, in certain bacteria, unique inositol-linked glycan and lipid structures have been reported. Although many reports of synthetic studies have been reported on glycan structure synthesis [2, 3], comparatively fewer reports address the comprehensive synthesis and the analysis of biological activity in relation to modifications of inositol or variations in the phospholipid moiety. Structures unique to microorganisms, related to lipid antigen presentation and immune activation, have been reported, and further development of synthetic methods as well as functional elucidation are expected in the future.