Tissue factor (TF) is the cellular receptor and cofactor for blood coagulation factor (F) VII. Exposure of flowing blood to cells that express TF leads to the initiation of blood coagulation. Blood coagulation is tightly regulated to generate a local fibrin clot at the site of vascular injury without compromising blood flow in the vasculature. This chapter describes the initiation and propagation of the response and how it is ultimately down-regulated to prevent widespread inappropriate blood coagulation.