Based on primary structure comparisons of their carbohydrate-recognition domains(CRDs), the superfamily of mammalian C-type lectins can be divided into six main families: proteoglycans, type Ⅱ transmembrane receptors, collectins, selectins, natural killer cell receptors and multi-CRD type Ⅰ transmembrane receptors, while all members of each family have homologous amino acid sequences, same overall molecular architecture and similar biological functions. The molecular basis for selective carbohydrate recognition by mammalian C-type lectins has been established at the primary to tertiary structure level of CRDs.