Astrocytes are possibly the most numerous cells of the vertebrate central nervous system, yet a detailed characterization of their functions is still missing. One potential reason for the obscurity of astrocytic function is that they represent a diverse population of cells that all share some critical characteristics. In the CNS, astrocytes have been proposed to perform many functions. For example, they are supportive cells that provide guidance to newly formed migrating neurons and axons. They regulate the functions of endothelial cells at the blood brain barrier, provide nutrients, and maintain homeostasis including ionic balance within the CNS. More recently, dissecting the central role of astrocytes in mediating injury responses in the CNS, particularly the spinal cord, has become an area of considerable importance. The ability to culture-enriched populations of astrocytes has facilitated a detailed dissection of their potential roles in the developing and adult, normal, and injured brain and spinal cord. Most importantly, in vitro models have defined molecular signals that may mediate or regulate astrocyte functions and the capacity to modulate these signals may provide new opportunities for therapeutic intervention after spinal cord injury and other neural insults.