Tissue factor (TF, coagulation factor III, CD142) is not only the main physiological initiator of normal blood coagulation, but is also important in the natural history of solid malignancies in that it potentiates metastasis and angiogenesis and mediates outside-in signalling. TF is expressed constitutively by many tissues which are not in contact with blood and by other cells upon injury or activation; the latter include endothelial cells, tissue macrophages, and peripheral blood monocytes. It can exist encrypted and unavailable functionally in the plasma membrane and the appearance of functional TF may be due to synthesis and/or de-encryption. Inflammatory cells often express TF and act to induce its production or de-encryption by other cells locally and, apparently, at remote sites. Inappropriate expression of TF by endothelial cells, macrophages or monocytes is thought to be an important trigger of coagulation in various pathological conditions. Several studies have shown that measurements of monocyte TF (mTF) may provide clinically significant information, particularly in patients with malignant and inflammatory diseases.