Pericytes (previously known as Rouget cells)[1] are multi-functional mural cells of the microcirculation that wrap around the endothelial cells that line the capillaries and venules throughout the body.[2] Pericytes are embedded in basement membrane, where they communicate with endothelial cells of the body's smallest blood vessels by means of both direct physical contact and paracrine signaling.[3] Pericytes help to maintain homeostatic and hemostatic functions in the brain and also sustain the blood–brain barrier.[4] These cells are also a key component of the neurovascular unit, which includes endothelial cells, astrocytes, and neurons.[5][6] Pericytes regulate capillary blood flow, the clearance and phagocytosis of cellular debris, and the permeability of the blood–brain barrier.