Glycosylation is the most abundant posttranslational protein modification. Specific glycans covalently attached to glycoproteins contribute to their functions, ensuring appropriate folding, secretion, half-life, and receptor-ligand interactions . Many different classes of glycans exist, but those discussed herein are the complex and hybrid N-glycans, core 1-derived O-glycans, and O-linked fucose glycans. The synthesis of each class of glycan is initiated by the addition of a single sugar, or group of sugars, to certain amino acids or amino acid sequons by specific glycosyltransferases via a particular linkage. The subsequent sugars are added individually in a carefully orchestrated pathway by specific glycosyltransferases that reside in the secretory compartments of the cell. Thus, the glycans ultimately synthesized by a cell depend on the cohort of glycosyltransferases, nucleotide sugar synthases, and transporters expressed by that cell, which will be influenced by metabolic state and stage of development. To determine roles for complex and hybrid N-glycans, core 1-derived O-glycans, and O-fucose glycans (Fig. 20.1) in oogenesis, fertilization, blastogenesis, implantation, and embryonic development, we used a maternal and zygotic gene-targeting approach.