In eukaryotes, the majority of cell surface and secreted proteins are covalently modified with carbohydrates. This type of posttranslational modification, glycosylation, is inherently complex exhibiting extensive chemical and conformational heterogeneity. Despite this complexity, there are common structural and biosynthetic principles. Here, we present an introduction to the different hierarchies of carbohydrate structure from stereochemistry of monosaccharides and their linkages to the structural diversity of complex mammalianglycosylation. These structures are discussed in the context of the glycan biosynthetic pathways, with an emphasis on N-linked glycosylation, and we outline the nomenclature with which these complex structures can be described. We describe the biosynthesis and crystal structures of antibodies and their glycans to illustrate the conformational properties of glycoprotein carbohydrates and how therapeutic antibodies are being developed by modulating these glycans.