Eph receptors and their ligands have been implicated in axonal pathfinding during the formation of neuronal networks. Whereas other guiding molecules, such as netrins and most semaphorins, are diffusible factors that can guide axons over considerable distances, Eph receptors and their ligands are cell-surface bound and are, therefore, involved in short-range contact-mediated guidance. Those molecules that have been analyzed appear to guide axons by repelling the growth cone, rather than attracting it. Here, we summarize the known biological functions of Eph receptors and ligands focusing on the developing nervous system, and we review the data on possible mechanisms of action.