Astrocytes constitute at least a third of all cells in human brains. Long thought to be passive support cells, astrocytes are recently found to be critical for the development and function of the central nervous system. Accumulating evidence show that astrocytes are involved in almost every type of neurological and psychiatric disorder. The cellular and molecular mechanisms that control astrocyte development as well as dysfunction of astrocytes in neurological and psychiatric disorders remains poorly understood. We combine cell culture and mouse genetic approaches to study astrocyte development in health and disease.