Glycation is a reaction in which free amino groups of proteins, lipids, and nucleotides are modified by monosaccharides. During the reaction, a Schiff base, Amadori products, various intermediate compounds, and eventually advanced glycation end products (AGEs) are formed. This sequence is also referred to as “nonenzymatic glycosylation” or the “Maillard reaction.” Glycation is a chemical reaction, one that is observed in a wide variety of circumstances including living body. It is often implicated as contributing to various pathological situations, especially diabetic complications and age-related changes. Proposed mechanisms by which glycation damages living cells include (1) impairment of target protein function directly by glycation, (2) increases in oxidative stress or carbonyl stress, and (3) activation of deleterious signal transduction pathways. Since there is no ultimate solution for the glycation-related pathogenesis at the present time, the clarification of the complete pathways of glycation will be helpful for developing new strategies. M. Takahashi (*) Department of Biochemistry, Sapporo Medical University School of Medicine, Sapporo, Japan e-mail: takam@sapmed.ac.jp # Springer Japan 2015 N. Taniguchi et al. (eds.), Glycoscience: Biology and Medicine, DOI 10.1007/978-4-431-54841-6_182 1339