Viruses bind to specific receptors on the surface of host cells through viral surface proteins and entry the cells. Virus receptors are divided into attachment receptors and entry receptors based on their functions. For example, the entry receptors for the human immunodeficiency virus (HIV) are CD4 and chemokine receptors (CCR5 or CXCR4), and these molecules directly contribute to the entry of HIV into cells. In recent years, it has been found that glycosaminoglycans (GAGs) bind to the surface proteins of various viruses and are involved in infection. For example, heparan sulfate on the cell surface not only plays various roles as an attachment receptor in the process of HIV adsorption and entry into cells but also can contribute to immune responses and pathogenesis [1, 2]. In addition, it has been reported that other pathogenic viruses and many insect-borne viruses also bind to GAGs [3], making virology a field closely related to glycoscience.