Skin is the largest organ of the human body and confers protection against mechanical and bacterial insults as well as thermoregulation. Seminal studies in anatomical description of blood supply, pharmacological manipulation of the circulation and the advent of anaesthesia and aseptic techniques in surgery led to a better understanding of skin flaps. Multiple anatomical and physiological factors that hamper adequate perfusion, before the collateral capillary network develops, can be detrimental for the flap survival. In general, flaps are divided into two main categories, based on whether the pedicle remains attached to the donor site or not; pedicled and free flaps, respectively. Although the fluid mechanics of blood flow are complex, certain factors applicable to the small vessels supplying the flap are well established. Resistance to lamina blood flow in a vessel is created by marginal adherence of molecules to the vessel wall.