The goal of this book is to integrate information that has accumulated in recent years revealing the active role of astrocytes in physiological processing in the central nervous system and to use this as a basis for identifying pathological roles for these glial cells in the brain. Astrocytes, a subtype of glial cell, have long been neglected as active participants in intercellular communication and information processing in the central nervous system, in part due to their lack of the electrical excitability. However, astrocytes possess a diverse assortment of ion channels, neurotransmitter receptors, and transport mechanisms that enable astrocytes to respond to many of the same signals that act on neurons. Since astrocytes can detect chemical transmitters that are released from neurons and can release extracellular signals, there is an increasing awareness that they play physiological roles in regulating neuronal activity and synaptic transmission. Astrocytes also play critical roles during pathophysiological states of the nervous system.