Astrocytes are specialized and heterogeneous cells that contribute to central nervous system function and homeostasis. However, the mechanisms that create and maintain differences among astrocytes and allow them to fulfill particular physiological roles remain poorly defined. We reveal that neurons actively determine the features of astrocytes in the healthy adult brain and define a role for neuron-derived sonic hedgehog (Shh) in regulating the molecular and functional profile of astrocytes. Thus, the molecular and physiological program of astrocytes is not hardwired during development but, rather, depends on cues from neurons that drive and sustain their specialized properties.