Since the discovery that nephron development depends on inductive signaling, the aim has been to characterize the signals involved. These have remained elusive, but some have been identified in recent years, indicating an important role for the members of the Wnt family of secreted growth and differentiation factors. Wnt-4, which is expressed in the developing nephron during the morphogenetic period, is necessary to form nephrons and Wnt signaling is also sufficient to trigger tubule development experimentally in the separated, uninduced kidney mesenchyme. The expression of several other Wnts during kidney development has also been characterized, establishing these as candidates for involvement in the mediation of mesenchymal-epithelial signaling and ureteric bud growth. The varied role of Wnt signaling in the developing kidney is discussed.