Changes in cytosolic Ca²⁺ concentrations evoke a wide range of cellular responses and intracellular Ca²⁺-binding proteins are the key molecules to transduce Ca²⁺ signaling via enzymatic reactions or modulation of protein/protein interations (Fig. 1). The EF hand proteins, like calmodulin and S100 proteins, are considered to exert Ca²⁺-dependent actions in the nucleus or the cytoplasm. The Ca²⁺/phospholipid binding proteins are classified into two groups, the annexins and the C2 region proteins. These proteins, distributed mainly in the cytoplasm, translocate to the plasma membrane in response to an increase in cytosolic Ca²⁺ and function in the vicinity of the membrane. Ca²⁺ storage proteins in the endoplasmic or sarcoplasmic reticulum provide the high Ca²⁺ capacity of the Ca²⁺ store sites, which regulate intracellular Ca²⁺ distribution. The variety and complexity of Ca²⁺ signaling result from the cooperative actions of specific Ca²⁺-binding proteins. This review describes biochemical properties of intracellular Ca²⁺-binding proteins and their proposed roles in mediating Ca²⁺ signaling.