Ketamine is an N-methyl-D-aspartate (NMDA) receptor antagonist with an enormous spectrum of indications across anesthesiology, critical care, emergency medicine, pain medicine, and psychiatry. Specific indications supported by the literature include acute surgical pain of moderate-to-severe intensity, especially in those patients who are opioid tolerant or with known obstructive sleep apnea; chronic pain, especially in the context of neuropathic states such as complex regional pain syndrome and spinal cord injury; mood disorders, especially treatment-resistant depression; and as adjunct therapy for opioid taper. Side effects are primarily related to its activity as an indirect sympathomimetic, and include bronchodilation, tachycardia, and hypertension, as well as hallucinations or vivid dreams, among others; at the subanesthetic doses relevant to this review, ketamine is generally well-tolerated. Although there is enormous variability in dosing strategies in the literature, baseline recommendations for dosing and patient monitoring are presented.