Magnetic resonance spectroscopy (MRS) measures the concentration of chemicals in the brain using conventional magnetic resonance imaging (MRI) scanners, thereby providing a “virtual biopsy” that is noninvasive, quantitative, and objective for the characterization of psychiatric disorders as well as other brain disorders. The primary chemicals relevant to psychiatry are N-acetylaspartate, a putative neuronal marker; glutamate, an excitatory neurotransmitter; γ-aminobutyric acid, an inhibitory neurotransmitter; and glutathione, an antioxidant involved in neuroinflammation. There exist different methods for measuring each of these metabolites using specialized pulse sequences, which will be described in detail. Finally, their biological roles and metabolism will be discussed in the context of psychiatric diseases such as schizophrenia, mood disorders, depression, and anxiety.