Proton magnetic resonance spectroscopy (1H MRS) employs the nuclear resonance phenomenon to provide biochemical information of the brain non-invasively. This methodology is increasingly being applied in clinical and pre-clinical research settings and has been found to play an important role in diagnosis, therapeutic evaluation and prognostic assessment of patients with different types of neurological and psychiatric diseases. This chapter first reviews the basic theory of 1H MRS and the biological significance of major brain metabolites that can be measured using 1H MRS. A summary of methodologies for acquisition, post-processing and quantification of 1H MRS follows, together with considerations concerning the design of protocols for obtaining good-quality data and discussions on currently available normative results. The last part of the chapter reviews a number of the current clinical applications that utilise 1H MRS of the brain. The results of these studies are valuable for differentiating between pathologies that show similar results on anatomic images, for assessing prognosis and for monitoring response to treatment.