Glycogen represents the largest energy reserve of the brain and is almost quite exclusively localized in astrocytes. In the first part of this article, a summary of our knowledge concerning brain glycogen metabolism and its regulation is presented. The second part focuses on potential evidence that glycogen can serve as energy substrate during neuronal activation, as well as on the role of brain glycogen as an emergency reserve in case of insufficient energy supply. These data are discussed in reference to the emerging concept of neuron–glia metabolic interactions