The endothelium, a delicate monolayer of cells lining all blood vessels, is a highly responsive sensoreffector organ, which through the secretion of a multitude of mediators, controls vascular tone, interacts with the inflammatory-coagulation cascades, promotes anti-aggregation, regulates immune cellular trafficking, and is crucial to angiogenesis. In brief, the endothelium is a major determinant of vascular homeostasis. It is easily damaged by intrinsic and extrinsic factors, and given its limited capacity for self-repair, is dependent on circulating bone marrow-derived endothelial progenitor cells for regeneration. There is increasing recognition that targeting the endothelium and maximizing inherent physiological function in the perioperative period may improve postoperative outcomes. This review explores the pathogenesis of endothelial dysfunction, the clinical utility of noninvasive methods to assess preoperative endothelial/microvascular (dys)function to improve risk stratification, and potential strategies for perioperative modulation of endothelial function.