Intracellular neuronal calcium sensors (NCS) constitute a rapidly growing family of calcium-binding proteins which belong to the superfamily of EF-hand proteins. The NCS family includes as subgroups the recoverins and GCAPs (guanylyl cyclase-activating proteins), which are primarily expressed in retinal photoreceptor cells, and the frequenins and VILIPs (visinin-like proteins), which are widely but differentially expressed in the nervous system. In this review the recent developments in elucidating the functional activities of NCS proteins on signal transduction pathways in neurons are surveyed and discussed. We will focus our attention on calcium-dependent membrane association by the so-called calcium-myristoyl switch as a possible mechanism of signal transduction and on the roles of NCS proteins in intraneuronal signaling cascades, which are best studied in the visual and olfactory systems.