Historically, brain catecholamine systems have been the primary focus of studies examining the neural substrates of drug addiction. In the past two decades, however, a wealth of evidence has accumulated indicating a pivotal role for glutamatergic neurotransmission in mediating addictive behaviors as well as long-term neuroplasticity associated with chronic drug use. As a result, there has been increased interest in developing glutamate-based therapies for the treatment of addictive disorders. Metabotropic glutamate (mGlu) receptors are classified into subcategories designated as Group I (mGlu1 and mGlu5), Group II (mGlu2 and mGlu3), and Group III (mGlu4, mGlu6, mGlu7, and mGlu8), and have received a great deal of attention due to their mediation of slower modulatory excitatory neurotransmission. Pharmacological ligands targeting these receptors have demonstrated reduced incidences of excitotoxicity or severe adverse side effects as compared to those targeting ionotropic glutamate (iGlu) receptors. Behavioral genetic and pharmacological studies have explored the role of individual mGlu receptor subtypes in regulating various addiction-related behaviours and several mGlu receptor ligands have been the subject of clinical testing for other medical conditions.