Neuregulin-1 beta 1/NRG1 beta 1 is one of many soluble and transmembrane NRG1 isoforms. All family members share an EGF-like domain that interacts with the ErbB family of tyrosine kinase receptors. NRG1 isoforms can be classified into type I (neu differentiation factor, NDF; heregulin, HRG; acetylcholine receptor inducing activity, ARIA), type II (glial growth factor, GGF) and type III (sensory and motor neuron-derived factor, SMDF) isoforms. NRG1 regulates multiple nervous system functions including neurotransmitter expression, axon guidance, synapse formation and plasticity, glial cell development, and axon myelination. It regulates heart morphogenesis and contractility and also plays a cardioprotective role following tissue injury. Multiple polymorphisms and aberrant expression of NRG1 isoforms are associated with the development of schizophrenia and many cancers.