The objective of this chapter is to introduce the shock. Shock occurs when the circulation of the arterial blood is inadequate to meet tissue metabolic needs, with resultant tissue hypoxia threatening damage to vital organs. The treatment must be directed both at its manifestations and its cause. Hypotension, tachycardia, oliguria and altered mental status are the cardinal features of shock syndrome. They are due to peripheral hypoperfusion and impaired oxygen delivery to the tissues. Often lactic acidosis complicates the clinical course of such patients. Hemorrhagic (hypovolemic) shock is the most common type of shock occurring in patients of polytrauma. Classification of shock, diagnosis of shock, laboratory studies, and treatment of shock are also discussed in this chapter. Treatment depends upon prompt assessment of the cause, type, severity, and duration of shock.