The brain is one of the most metabolically active organs of the human body. In addition to an extensive glucose metabolism, an intense amino acid metabolism occurs in brain due to protein turnover and the synthesis and degradation of amino acids and amino acid-derived neurotransmitters. Due to cell type compartimentation of metabolic pathways energy is not wasted by equiping every brain cell type with every metabolic pathway. However, the loss of independence is the price the different cell types in the brain have to pay for a close coupling due to specialization for different functions. During the last two decades evidence is growing that an intensive metabolic exchange occurs between the different types of brain cells. The dependence of neurons on metabolites of astrocytes strongly suggest a metabolic cooperation between the neighboring cell types of the brain rather than competition of these cell types for extracellular substrates. Strong evidence on metabolite trafficking between astrocytes and neurons has been obtained for the metabolism of carbohydrates and amino acids as well as for the defense against xenobiotics and oxidative stress. A good example for a metabolic interaction between astrocytes and neurons is the supply of neurons by astrocytes with precursors for the synthesis of the protective tripeptide glutathione (GSH).