Glycans are vital components of glycoproteins, glycolipids, and proteoglycans in all domains of life. Glycoproteins are grouped by the type of carbohydrate and amino acid linkage site. N-linked glycosylation is a modification of asparagine, whereas O-linked glycosylation occurs through the hydroxyl group of serine and threonine residues. Glycosylation occurs co- or post-translationally on >50% of eukaryotic proteins resulting in membrane-associated, intracellular, or secreted glycoproteins that are crucial in cellular processes, protein bioactivity and metabolic turnover. Modification by O-linked-N-acetyl glucosamine (O-GlcNAc) has rapidly emerged as a major cellular signaling mechanism with number of modified targets similar to protein phosphorylation. Many oncogenes and tumor supressors are regulated by O-GlcNacylation. O-GlcNAc modification is ubiquitous among eukaryotes, from yeast to humans and its modifying enzymes have been well characterized. O-GlcNAc modified nuclear and cytosolic targets include: transcription factors, signaling proteins, metabolic enzymes, mitochondrial trafficking, cell cycle regulation, glucose homeostasis. O-GlcNAc glycosylation is implicated in normal brain functions, etiology of neurodegeneration, type II diabetes, and pathways involved in morphogenesis and virulence factors of microbes and plant host cells. Since glycoproteins are not directly encoded in the genome, methods of characterization and analyses of glycoproteins are of great interest.