Recent research has seen low-dose ketamine emerge as a novel, rapid-acting antidepressant. Ketamine, an N-methy-d-aspartate (NMDA) receptor antagonist, leads to effects on the glutamatergic system and abnormalities in this neurotransmittor system are present in depression. This article aims to (1) review the clinical literature on low-dose ketamine as a rapid-acting antidepressant in affective disorders, (2) provide a critical overview of the limitations of ketamine and research attempts to overcome these (3) discuss the proposed mechanisms of action of ketamine and (4) point towards future research directions.