This article provides a comprehensive review of the classifications and types of shock that can occur following trauma, surgery, organ damage/disease (neurogenic, hypovolaemic, cardiogenic) or during/following treatment (septic, anaphylaxis) and the stages (compensatory, progressive and irreversible) of shock. It provides an overview of the physiological changes that occur in the cell, at organ level, to oxygen consumption and demand, and coagulation.