This issue of Hematology/Oncology Clinics of North America, guest edited by Dr. Robert Brodsky, is devoted to Complement-mediated Hemolytic Anemias. Articles in this outstanding issue include: Complement: An overview for the clinician; Warm autoimmune hemolytic anemia; Cold Agglutinin Disease; ABO incompatible blood transfusions; Paroxysmal cold hemoglobinuria; Paroxysmal nocturnal hemoglobinuria; Congenital CD59 deficiency; Atypical Hemolytic Uremic Syndrome (HUS); Typical Hemolytic Uremic Syndrome (HUS); Thrombotic thrombocytopenic purpura; and Pharmacologic complement inhibitors.