The galectin-1 protein is 135 amino acids in length and highly conserved across species. It can be found in the nucleus, the cytoplasm, the cell surface and in the extracellular space. Galectins, in general, lack a traditional signal sequence but are still secreted across the plasma membrane. Although galectins in general, and Gal-1 in particular, were first described as lectins that bind β-galactosides, it is now clear from the literature that as well as being a lectin, Gal-1 is also engaged in many protein-protein interactions. Gal-1 plays a number of crucial roles in neuronal cell differentiation and survival in both the central and the peripheral nervous systems, and the establishment and maintenance of T-cell tolerance and homeostasis in vivo.