Virchow's triad presents the three broad categories of factors that are thought to contribute to thrombosis.

The triad consists of:

1. Alterations in normal blood flow
2. Injuries to the vascular endothelium
3. Alterations in the constitution of blood (hypercoagulability)

Alteration in blood flow can include turbulence, stasis, mitral stenosis, and varicose veins. Injuries to the vascular endothelium can be cause by damage to the veins arising from shear stress or hypertension.
Hypercoagubility can be a consequence of numerous possible risk factors such as hyperviscosity, deficiency of antithrombin III, nephrotic syndrome, changes after severe trauma or burn, disseminated cancer, late pregnancy and delivery, race, age, smoking, and obesity.

Virchow's triad was first formulated by the German physician Rudolf Virchow (1821-1902) in 1856.