As shown in Fig. 38.1, glycosaminoglycans (GAGs) refer to the glycan parts of proteoglycans (PGs), which are a type of glycoconjugate. Based on their constituent sugars and linkage patterns, GAGs are classified into chondroitin sulfate, dermatan sulfate, heparan sulfate, keratan sulfate, and hyaluronan. They are further divided into subclasses based on the sulfation patterns of the repeating disaccharide units except for hyaluronan. Since GAGs are located on the exterior of PGs, they are considered to be the functional sites responsible for physiological activities. As represented by the heparin pentasaccharide, which has high affinity for antithrombin III (ATIII), GAG exhibits biological activities even at the oligosaccharide level. Consequently, many GAG oligosaccharides have been chemically synthesized to date [1–3]. The advantages of synthetic glycans include structural precision, uniformity, scalability, and the ability to generate analogs. Recently, chemical synthesis has been achieved for many functional GAG oligosaccharides.