This chapter focuses on astrocytes, a subtype of glial cell, which exhibit a form of excitability based on intracellular Ca2+ elevations that can stimulate glutamate release from astrocytes. The mechanism underlying this release is exocytosis. Astrocytes express the protein components of the exocytic-secretory machinery, including the core fusion complex as well as the transporters and pumps necessary for filling astrocytic vesicles with glutamate. The characteristics of exocytosis in astrocytes are distinct from those observed in neurons because of differences in the expression of the subtypes of exocytic protein subtypes. The morphological arrangements of the exocytic secretory machinery and the functional neurotransmitter receptors in astrocytic processes enable them to receive signals, focally, from adjacent synaptic terminals and respond back to terminals/dendrites via exocytic glutamate release. Astrocytes have the potential to play an active role in the computational power of the brain. © 2007 Elsevier Inc. All rights reserved.