It is known that changes in specific glycans can alter the functions of proteins and cells and cause the onset or worsening of diseases. Therefore, it is believed that visualizing (imaging) specific glycans can reveal the functions and states of proteins, cells, and individuals and can be useful in diagnosing diseases. Currently, methods combining metabolic labeling with sugar analogs and click chemistry [1–3] and methods of tracing chemically labeled glycolipids and glycoproteins incorporated into cells are used [4] (Fig. 25.1). Recently, attempts to label specific enzyme product glycans using click chemistry in combination with mutant glycosyltransferases (bump-and-hole engineering) [5] have also been used.