Over the last years numerous studies have focussed on the in vivo expression of tissue factor (TF) in health and disease. The selective perivascular distribution of TF and the lethal effects of TF knockouts have added strong support to the widely accepted view that TF plays a pivotal role in the initiation of blood coagulation during physiological hemostasis. Inappropriate in vivo expression of TF, particularly by cells that do not express this protein under normal conditions (mainly monocyte-macrophages and endothelial cells), has been documented and is likely responsible for fibrin deposition in a variety of pathological conditions, among which sepsis-associated disseminated intravascular coagulation (DIC) and thromboembolic disease. In malignancy, in vivo expression of TF by tumor cells and/or by host cells has been implicated not only in intratumoral and systemic activation of blood coagulation but also in tumor growth and dissemination.