Ephrin-B1 is a protein that in humans is encoded by the EFNB1 gene. This gene encodes a member of the ephrin family. The encoded protein is a type I membrane protein and a ligand of Eph-related receptor tyrosine kinases. It may play a role in cell adhesion and function in the development or maintenance of the nervous system. Mutations in this protein are responsible for most cases of craniofrontonasal syndrome.