The pathophysiology underlying the initiation and progression of cardiovascular disorders is highly complex and multifactorial. The endothelium also plays a crucial role in the pathogenesis of thrombogenesis and atherogenesis, and a continuum of endothelial activation, dysfunction or damage is evident in many cardiovascular disorders both at the macro and microscopic level(s). This review article aims to provide an overview of the assessment of endothelial (dys)function and discuss the implications and limitations of such assessments.