Contactin 1, also known as CNTN1, is a member of the immunoglobulin superfamily. It is a glycosylphosphatidylinositol (GPI)-anchored neuronal membrane protein that functions as a cell adhesion molecule. It may play a role in the formation of axon connections in the developing nervous system. Chick contactin (also known as F11 in the chick and F3 in the mouse) is a neuronal cell adhesion molecule of the immunoglobulin superfamily that is composed of 6 C2 Ig domains and 4 fibronectin type III (FN-III) repeats. In the developing mouse cerebellum, contactin is confined to discrete neuronal subpopulations and subcompartments, for example, the granule cell axons, Golgi cells, and mossy fibers, while in contrast, stellate cells and Purkinje cell bodies and dendrites are devoid of contactin expression.