Mood disorders are grouped into four broad categories: depressive disorders, bipolar disorders, mood disorder due to a general medical condition, and substance-induced mood disorders. This chapter provides some guidelines on the assessment and management of mood disorders in the emergency department (ED) setting. Cardiovascular diseases, such as coronary artery disease, myocardial infarction, and stroke, are also often associated with depression. The diagnosis of a mood disorder is based on history, collateral information, and observation of the patient's behavior. Mood disorders should be suspected in patients with multiple, vague, nonspecific complaints and in patients who are frequent users of medical care. The creation of a safe and stable environment for the patient should be a first priority in management. The patient with an acute manic episode may be disruptive, refuse medical evaluation, and make repeated attempts to leave the ED.