In mammals, leucocytes of the adaptive and innate immune systems must move from their sites of origin to sites of maturation, or to where they are deployed against the invasion of pathogens. The vascular tree serves as the primary throughfare by which leucocytes move to these various destinations. Adhesion must be established between the leucocyte and the endothelial cells that line the vascular tree to enable leucocytes to escape the vascular compartment and then contribute to extravascular immune processes. A major fraction of these leucocyte-endothelial-cell adhesive events initiate with, and require interactions between, the selectin family of cell adhesion molecules and their glycoconjugate counter-receptors. This article will review the structures of the glycan components of these counter-receptors, and the glycosyltransferases that control their expression.