Millions of units of blood products are transfused annually to patients in the United States. Red blood cells are transfused to improve oxygen-carrying capacity in patients with or at high risk of developing symptomatic anemia. Restrictive transfusion thresholds with lower hemoglobin levels are typically clinically equivalent to more liberal thresholds. Transfusion of plasma corrects clinically significant coagulopathy in patients with or at high risk of bleeding. Mildly abnormal laboratory coagulation values are not predictive of clinical bleeding and should not be corrected with plasma. Transfused platelets prevent or treat bleeding in patients with thrombocytopenia or platelet dysfunction. Cryoprecipitate is transfused to treat hypofibrinogenemia. Many adverse reactions can occur during or after blood product transfusion. Transfusion-associated circulatory overload (i.e., volume overload) is the most common cause of mortality associated with blood products. Modifications to blood products can prevent or decrease the risks of transfusion-related adverse reactions. It is critical to quickly recognize when a reaction is occurring, stop the transfusion, assess, and support the patient. Reporting a reaction to the blood bank is part of ensuring patient safety and supporting hemovigilance efforts.