The common features of all different kinds of circulatory shock are a disturbance of the microcirculation and an imbalance between cellular oxygen demand and supply. The pathophysiology is discussed by the example of hypovolemic-hemorrhagic shock, including macrocirculation, humoral regulatory mechanisms, the role of vascular endothelium, and cellular dysfunction. The first aim of therapeutic efforts is the rapid restitution of a normal circulatory volume as a basic requirement for the normalisation of the microcirculation. Actual concepts of volume substitution and transfusion therapy are presented.