Early specification of progenitors of the ventral spinal cord involves the morphogen Sonic Hedgehog which induces distinct progenitor identities in a dose-dependent manner. Following these initial patterning events, progenitor identities have to be maintained and propagated faithfully in order to generate appropriate numbers of progeny. Here we provide evidence that local communication via Eph:ephrin signaling is required to maintain progenitor identities at progenitor domain boundaries. We show that ephrinB2 and ephrinB3 are expressed in restricted progenitor domains in the ventral spinal cord while Eph receptors are more broadly expressed. Genetic loss-of-function analyses indicate that expression of ephrinB2 and ephrinB3 is required to control progenitor identities and in vitro experiments reveal that activation of EphA4 in spinal progenitors up-regulates the expression of the identity transcription factor Nkx2.2. Altogether our results indicates that local cell-to-cell communication is necessary to control progenitor identity at domain boundaries.