C-type lectins (CTLs) are Ca++-dependent glycan-binding proteins (GBPs) that share primary and secondary structural homology in their carbohydrate-recognition domains (CRDs). The CRD of CTLs is more generally defined as the CTL domain (CTLD), because not all proteins with this domain bind either glycans or Ca++. CTLs include collectins, selectins, endocytic receptors, and proteoglycans, some of which are secreted and others are transmembrane proteins. They often oligomerize, which increases their avidity for multivalent ligands. CTLs differ significantly in the types of glycans that they recognize with high affinity. These proteins function as adhesion and signaling receptors in many pathways, including homeostasis and innate immunity, and are crucial in inflammatory responses and leukocyte and platelet trafficking.