Endothelial barrier function refers to the ability of the cells lining blood vessels, known as endothelial cells, to control the exchange of substances between the bloodstream and surrounding tissues. This barrier function is crucial in maintaining homeostasis within the body, as it allows essential nutrients and oxygen to reach tissues while preventing harmful substances and pathogens from entering the bloodstream. Disruption of endothelial barrier function can lead to a variety of health complications, such as inflammation, edema, and increased risk of cardiovascular diseases. As such, research in this area focuses on understanding the mechanisms that regulate endothelial barrier function and developing strategies to protect or restore this barrier in various disease conditions. Techniques such as in vitro cell culture models, animal models, and advanced imaging technologies are commonly used in studying endothelial barrier function.