Anemia is a common worldwide problem that is associated with nonspecific complaints. The initial focus for the emergency evaluation of anemia is to determine whether the problem is acute or chronic. Acute anemia is most commonly associated with blood loss, and the patient is usually symptomatic. Chronic anemia is usually well tolerated and is often discovered coincidentally. Once diagnosed, the etiology of anemia can often be determined by applying a systematic approach to its evaluation. The severity of the anemia impacts clinical outcomes, particularly in critically ill patients; however, the specific threshold to transfuse is uncertain. Evaluation of the current literature and clinical guidelines does not settle this controversy, but it does help clarify that a restrictive transfusion strategy (ie, for patients with a hemoglobin < 6-8 g/dL) is associated with better outcomes than a more liberal transfusion strategy. Certain anemias may have well-defined treatment options (eg, sickle cell disease), but empiric use of nutritional supplements to treat anemia of uncertain etiology is discouraged.