Contactins compose a subgroup of the Ig superfamily of cell adhesion molecules. This molecule group consists of Contactin-1, Contactin-2/TAG-1, Contactin-3/BIG-1, Contactin-4/BIG-2, Contactin-5/NB2, and Contactin-6/NB3. Members of the Contactin family share a common molecular structure which includes six Ig-like and four fibronectin type-III extracellular domains and a glycosylphosphatidylinositol (GPI) anchor. Contactins exert critical effects during development and in the adult nervous system. Their actions influence essential biological processes including neural migration, adhesion, and differentiation, and neurite outgrowth and fasciculation. With the exception of Contactin-2, which is expressed earlier, Contactin expression commences postnatally. Because Contactins are expressed on axons and are known to promote neurite outgrowth, initial studies investigated the role of Contactins in axon guidance and cell migration.