In the mammalian brain, a major regulatory peptide is vasoactive intestinal peptide (VIP). This 28 amino acid peptide, originally isolated from the porcine duodenum, was later found in the central and peripheral nervous systems and in endocrine cells, where it exhibits neurotransmitter and hormonal roles. Increasing evidence points to VIP's importance as a mediator or a modulator of several basic functions. Thus, VIP is a major factor in brain activity, neuroendocrine functions, cardiac activity, respiration, digestion, and sexual potency. In view of this peptide's importance, the mechanisms controlling its production and the pathways regulating its functions have been reviewed. VIP is a member of a peptide family, including peptides such as glucagon, secretin, and growth hormone releasing hormone. These peptides may have evolved by exon duplication coupled with gene duplication. The human VIP gene contains seven exons, each encoding a distinct functional domain on the protein precursor or the mRNA. VIP gene transcripts are mainly found in neurons or neuron-related cells. VIP gene expression is regulated by neuronal and endocrine signals that contribute to its developmental control. VIP exerts its function via receptor-mediated systems, activating signal transduction pathways, including cAMP. It can act as a neurotransmitter, neuromodulator, and a secretagog. As a growth and developmental regulator, VIP may have a crucial effect as a neuronal survival factor. We shall proceed from the gene to its multiple functions.