Metabotropic glutamate receptors (mGluRs) are a novel family of recently cloned G protein-coupled receptors. These receptors are heterogeneous and coupled to multiple second messenger systems that include increases in phosphoinositide hydrolysis, activation of phospholipase D, decreases in cAMP formation, increases in cAMP formation, and changes in ion channel function. Using the selective mGluR agonist 1-aminocyclopentane-1,3-dicarboxylic acid (1s,3R-ACPD), considerable progress has been made towards understanding the role of this glutamate receptor class in the central nervous system. This article reviews the molecular aspects and pharmacology of mGluRs, and recent studies elucidating their role in brain function and pathology.