In a variety of cell types, activation of phospholipase C-linked receptors results in the generation of intracellular Ca2+ signals comprised of components of both intracellular Ca2+ release, and enhanced entry of Ca2+ across the plasma membrane. This entry of Ca2+ occurs by either of two general mechanisms: the release of stored Ca2+ can activate, by an unknown mechanism, storeoperated channels in the plasma membrane, a process known as capacitative calcium entry. Alternatively, second messengers generated at the plasma membrane can activate Ca2+ channels more directly, a non-capacitative calcium entry process. This review summarizes current knowledge of the underlying signaling mechanisms and the nature of the channel molecules responsible for these two general categories of regulated Ca2+ entry.