Despite improved understanding of the pathophysiology of shock and significant advances in technology, it remains a serious problem associated with high morbidity and mortality. Early treatment is essential but is hampered by the fact that signs and symptoms of shock appear only after the shock state is well established and the body's compensatory mechanisms have started to fail. Although the causes of shock are varied, the basic abnormality in all varieties is tissue and cellular dysoxia. In this overview we discuss the definition, classification and pathogenesis of shock in light of the recent advances in our understanding of its mechanisms. The epidemiology, diagnosis, and management of the various types of shock are also briefly discussed.