Abstract Astrocytes constitute approximately 30 percent of cells in the CNS and are the most abundant glial cells. They constitute a structural and functionally heterogeneous population and are critically involved in development, homeostasis, synaptic and neuronal network activity, and response to injury and repair in the CNS. They have a major role in synaptic formation during development and maintenance of extracellular fluid and potassium homeostasis, antioxidant protection, metabolic support to active neurons and oligodendrocytes, local regulation of cerebral blood flow, uptake and recycling of synaptic glutamate and γ-aminobutyric acid (GABA), synaptic plasticity, and coordination of activity in neuronal networks in the adult CNS. Astrocytes are primarily affected in metabolic, genetic, and immune astrocytopathies and have a major role in the pathophysiology of epilepsy and in vascular, immune, inflammatory, and neurodegenerative disorders.