This is a second edition of a book that provides an overview of the most current findings on the diverse roles played by astrocytes in the function and dysfunction of the central nervous system (CNS), with emphasis on their cellular connections. Astrocytes are highly elaborated cells and likely the only neural cells that simultaneously establish associations with different cellular types. The fine processes of astrocytes are found in practically all nearby cellular types in the CNS, including astrocytes themselves, neurons, oligodendrocytes, microglia, and brain endothelial cells. Such close morphological associations, together with the fact that astrocytes express a multitude of ion channels, transporters, and membrane receptors, endow these cells with the unique capability to sense and influence diverse CNS functions. Disruption of these elaborated connections and altered astrocyte polarization are implicated in numerous pathological conditions, such as epilepsy, stroke, leukodystrophies, Alzheimer’s, and autism, and also certain psychiatric disorders, major depression, and schizophrenia.