Research on immunity and commensal bacteria in the gut is attractive as one of the important research fields in life science. It is known that α1,2-fucose, a glycan expressed on the host’s epithelial cells in gastrointestinal tracts, interacts with resident luminal microbes, not only forming the basis for symbiosis in the intestine but also being involved in infections by pathogenic microbes [1] (Fig. 69.1). In addition, the non-sense polymorphism of fucosyltransferase 2 (Fut2), one of the glycosyltransferases that control α1,2-fucosylation, in humans is known to disrupt the intestinal microbiota and is related to the development of various diseases such as infectious diseases, Crohn’s disease, and type 1 diabetes [2]. Therefore, it is important to understand the role of glycans in host epithelial and immune cells that confront and interact with luminal microbes in the gut in glycoscience, from the perspectives of basic science and clinical research (Fig. 69.1).