The cardiovascular system is the first functional organ system to develop in the vertebrate embryo. Embryonic growth and differentiation essentially depend on transport of nutrients and waste through the early vasculature, and certain events in morphogenesis are thought to be influenced by the hemodynamic forces of the beating heart. The vasculature not only serves as a 'nutrient and waste pipeline' but is also a major communication system between distant organs and tissues. The vascular endothelial cell mediates vascular growth, permeability, integrity and interactions with blood cells. In most tissues the endothelium itself is highly specialized to meet the particular needs of the tissue in terms of quality and quantity of incoming and outgoing molecules and messages. The areas covered by Morphogenesis of the Endothelium include the formation of blood vessels in embryonic tissues by vasculogenesis and angiogenesis and the differentiation of endothelium in organs.