Tyrosine kinase receptors and their ligands allow communication between cells in the developing and adult organism. An extensive line of research has revealed that ‘neuregulins’, a family of EGF-like factors that signal via ErbB receptors, are used frequently for cell communication during nervous system development, and control a spectacular spectrum of developmental processes. For instance, during development of the peripheral nervous system, Schwann cells require neuronally-produced neuregulin (Nrg1) for growth, migration and myelination, neural crest cells rely on mesenchymally-generated Nrg1 signals for migration, while muscle requires neuronally-produced Nrg1 for the differentiation of a muscle spindle. In the central nervous system, neuregulin signals allow cells to act as guideposts or as barriers for axons during pathfinding. Neuregulin signals are also important in other organs, but the nervous system functions have received recently considerable attention due to the finding that particular haplotypes of Nrg1 and ErbB4 predispose to schizophrenia. Understanding the neuregulin signaling system can thus contribute to define causes of this devastating mental disorder.