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This important chapter reviews basic vascular anatomy and physiology. The vascular system is part of the cardiovascular system, which maintains blood supply to all organs and tissues to upkeep human metabolic activities. The vascular system has three components: arteries, veins, and capillaries. These components are where oxygen, nutrients, and metabolites exchange. Vascular wall biology has been a very hot topic for the last decades because it is involved in numerous physiological and pathological processes, yet many aspects remain unknown. There are three layers in the vascular wall: tunica intima, tunica media, and tunica adventitia. Adventitia has mainly collagenous and elastic fibers, and its physiological function was mostly unknown until recently; it is believed to be involved in the pathogenesis of atherosclerosis. The vascular tone can be altered by neurohumoral and other factors. The brain, the heart, and other vital organs have the capability to regulate their blood flow via a phenomenon called autoregulation, which maintains relatively constant blood flow to vital organs over a wide range of perfusion pressures.