Shock is a syndrome of poor tissue perfusion that causes imbalance of oxygen demand and oxygen supply. Delayed diagnosis and treatment of shock may increase morbidity and mortality of the patients. With a through knowledge in circulatory physiology and pathophysiology in each form of shock, the outcome of the patients would be improved. In general, shock usually occurs with hypotension. Blood pressure depends on adequate preload, afterload and also cardiac contractibility. The alteration of any factor can cause hypotension. Shock can be divided into 4 types, hypovolemic, cardiogenic, distributive and mixed type, depending on its pathophysiology. Through history taking and physical examination can differentiate each type of shock. The main principle of treatment in shock is to evaluate preload, afterload and cardiac contractility. The adequacy of preload should be evaluated by fluid challenge test. Intravenous fluid, either colloid or crystalloid, give the same result in the patients in order to keep adequate intravascular volume and have no significant difference in morbidity and mortality. The afterload and cardiac contractility can be evaluated by other special techniques, for example echocardiogram and cardiac output measurement. Furthermore, vasoactive drugs, such as dopamine, dobutamine and norepinephrine, are the mainstay of shock management particularly in cardio-genic and septic shock. The good selection and appropriate use of vasoactive drug is also important. In addition, the complications of shock, for instance metabolic acidosis, acute renal failure, should be promptly treated. The mortality and morbidity of shock would be improved when physicians make the appropriate diagnosis and management on the basis of normal physiology.