IRBIT (IP(3)Rs binding protein released with IP(3)) is a protein originally identified by the Mikoshiba group as an inhibitor of IP(3) receptors function. Subsequently it was found to have multiple functions and regulate the activity of diverse proteins, including regulation of HCO(3)(-) transporters to coordinate epithelial HCO(3)(-) secretion and to determine localization of the Fip1 subunit of the CPSF complex to regulate mRNA processing. This review highlights the remarkably divers functions of IRBIT that are likely only a fraction of all the potential functions of this protein.