The term hemophilia is used to refer to a group of blood coagulation disorders that result from deficiencies in specific plasma clotting factors. Names were assigned to the various coagulation factors by the International Committee on Thrombosis and Hemostasis (ICTH) in 1962: the factor missing in hemophilia A was subsequently termed factor VIII. A scheme for the interaction of the various factors in a coagulation pathway was independently devised by two groups shortly thereafter. Of all causes of hemophilia, types A and B are most associated with intraosseous and intraarticular bleeding. Hemophilia A (classic hemophilia) results from a deficiency of factor VIII. Hemophilia B (Christmas disease) is due to a functional deficiency of plasma thromboplastin component (factor IX).