EPHA1 or EPH receptor A1 belongs to the ephrin receptor subfamily of the protein-tyrosine kinase family. Receptors in the EPH subfamily typically have a single kinase domain and an extracellular region containing a Cys-rich domain and 2 fibronectin type III repeats. An important role of Eph receptors and their ligands ephrins is to mediate cell-contact-dependent repulsion. Eph receptors and ephrins also act at boundaries to channel neuronal growth cones along specific pathways, restrict the migration of neural crest cells, and via bidirectional signaling prevent intermingling between hindbrain segments. Eph receptors and ephrins can also trigger an adhesive response of endothelial cells and are required for the remodeling of blood vessels. Eph receptors and ephrins have emerged as key regulators of the repulsion and adhesion of cells that underlie the establishment, maintainence, and remodeling of patterns of cellular organization. The ephrins and Eph receptors are implicated as positional labels that may guide the development of neural topographic maps.