Ca2+ mediates the effect of many hormones, neurotransmitters and growth factors on contractility and motility, carbohydrate metabolism, cell cycle, gene expression and neuronal plasticity. Multifunctional Ca2+/calmodulin-dependent (CaM) kinase, CaM kinase Ia, CaM kinase Ib and CaM kinase IV are four of the kinases that mediate Ca(2+)-signaling pathways. Recent studies have clarified our understanding of their structure, regulation and function.