Astrocytes exhibit several unique metabolic features. They possess a reserve glycolytic capacity that is used to cope with the burden of gultamate recycling. They contain glycogen stores that can be mobilized to face high energy demands following intense neuronal activity. Astrocytes also play a pivotal role in the protection against radical oxygen species, notably by providing precursors for the synthesis of glutathione to neurons. In addition, they are essential to replenish the neuronal glutamate pool and maintain glutamatergic transmission by providing the precursor gultamine synthesized either from recycled gultamate or de novo from gulcose. Together with synaptic elements, astrocytes constitute a metabolic unit of fundamental importance to ensure excitatory neurotransmission.