Astrocytes can exocytotically release the gliotransmitter glutamate from vesicular compartments. Increased cytosolic Ca²⁺ concentration is necessary and sufficient for this process. The predominant source of Ca²⁺ for exocytosis in astrocytes resides within the endoplasmic reticulum (ER). Inositol 1,4,5-trisphosphate and ryanodine receptors of the ER provide a conduit for the release of Ca²⁺ to the cytosol. The ER store is (re)filled by the store-specific Ca²⁺-ATPase. Ultimately, the depleted ER is replenished by Ca²⁺ which enters from the extracellular space to the cytosol via store-operated Ca²⁺ entry; the TRPC1 protein has been implicated in this part of the astrocytic exocytotic process. Voltage-gated Ca²⁺ channels and plasma membrane Na⁺/Ca²⁺ exchangers are additional means for cytosolic Ca²⁺ entry. Cytosolic Ca²⁺ levels can be modulated by mitochondria, which can take up cytosolic Ca²⁺ via the Ca²⁺ uniporter and release Ca²⁺ into cytosol via the mitochondrial Na⁺/Ca²⁺ exchanger, as well as by the formation of the mitochondrial permeability transition pore. The interplay between various Ca²⁺ sources generates cytosolic Ca²⁺ dynamics that can drive Ca²⁺-dependent exocytotic release of glutamate from astrocytes. An understanding of this process in vivo will reveal some of the astrocytic functions in health and disease of the brain.