Ketamine is unique among anesthetics and analgesics. The drug is a rapid-acting general anesthetic that produces an anesthetic state characterized by profound analgesia, preserved pharyngeal-laryngeal reflexes, normal or slightly enhanced skeletal muscle tone, cardiovascular and respiratory stimulation, and occasionally a transient and minimal respiratory depression. Research has demonstrated the efficacy of its use on anesthesia, pain, palliative care, and intensive care. Recently, it has been used for postoperative and chronic pain, as an adjunct in psychotherapy, as a treatment for depression and posttraumatic stress disorder, as a procedural sedative, and as a treatment for respiratory and/or neurologic clinical conditions. Despite being a safe and widely used drug, many physicians, such as intensivists and those practicing in emergency care, are not aware of the current clinical applications of ketamine. The objective of this narrative literature review is to present the theoretical and practical aspects of clinical applications of ketamine in intensive care unit and emergency department settings.