The renin-angiotensin-aldosterone system (RAAS) is a neuroendocrine complex system that regulates the modulation of salt and water homeostasis, and regulation of blood pressure. Through its multiple interactions it protects the endothelium, heart, brain and kidney. In addition, the RAAS regulates the vascular response to injury and inflammation. Chronic activation/dysregulation of the RAAS leads to hypertension and perpetuates a cascade of proinflammatory, prothrombotic and atherogenic effects associated with endorgan damage (heart, brain, kidney, endothelium). Consequently, the RAAS is an important therapeutic target in these situations. This article presents an overview of physiology, pathophysiology and pharmacologic modulation of the RAAS.