Almost 150 years ago, the German pathologist Virchow4 postulated that thrombosis was due to stasis of the blood, changes in the vessel wall, and changes in the composition of blood. Certain risk factors for VTE have been known for some time, including surgery, trauma, malignant neoplasms, immobility sepsis, congestive heart failure, nephrotic syndrome, obesity, varicose veins, postphlebitic syndrome, oral contraceptives, and estrogens. However, Virchow's "changes in composition of the blood," or thrombophilia (also known as hypercoagulability), was not described until 1965, when Egeberg5 described inherited anti–thrombin III deficiency. In the 1980s, deficiencies of the anticoagulant proteins, protein C and protein S, were also found to be causes of inherited thrombophilia.6,7 However, these inherited deficiencies accounted for only 5% to 15% of VTE8 (Table 1). Subsequently, the antiphospholipid antibody syndrome has been associated with not only venous thrombosis but also arterial thrombosis.10 Over the past few years, considerable progress has been made in describing inherited and other causes of this disorder. In this review, we will discuss recent advances in diagnosing these newly described inherited and acquired disorders.