Human endothelial cells form the inner lining of a blood vessel and provides an anticoagulant barrier between the vessel wall and blood. Endothelial cells also generate an antithrombotic surface that facilitates transit of plasma and cellular constituents throughout the vasculature. As a selective permeability barrier, the endothelial cell is a unique multifunctional cell with critical basal and inducible metabolic and synthetic functions. The endothelial cell reacts with physical and chemical stimuli within the circulation and regulates hemostasis, vasomotor tone, and immune and inflammatory responses. In addition, the endothelial cell is pivotal in angiogenesis and vasculogenesis.