In the past, endothelium was thought to be only a mechanical barrier. Today, endothelium is known to be a tissue regulating vascular tone, cell growth and the interaction between the leukocytes, thrombocytes and the vessel wall. It also synthesizes growth factors and thrombo-regulatory molecules and responds to physical and chemical signals. Even though the term "endothelial dysfunction" is generally used for deterioration of endothelium-dependent vasodilatation; the term also includes the abnormalities between endothelium and leukocytes, thrombocytes and regulatory molecules and conditions resulting in aberrant endothelium activation. Healthy endothelium is essential for cardiovascular control. Thus, it plays an important role in pathogenesis of many diseases and cardiovascular problems such as atherosclerosis, systemic and pulmonary hypertension, cardiomyopathies and vasculitides. The aim of this chapter is to explain endothelial dysfunction and the circulating molecules of endothelial cells as they become potential targets of therapeutic approach for hypertension. This chapter reviews the roles of endothelial dysfunction in hypertension by addressing (1) the nature of endothelial function, (2) mechanisms of endothelial dysfunction and its relationship with the diseases (3) also endothelial function testing (4) the role of endothelial dysfunction and hypertension and (4) the effects of antihypertensive therapeutic options on the endothelial dysfunction. In addition to these, the role of endothelial dysfunction in white coat hypertension has been discussed. The key connections between hypertension and endothelial dysfunction are vitally important for future studies to permit new interventions to be designed and released.