The balance of power is one of the most fundamental concepts behind international politics and provides a structure for explaining some of the essential principles behind international relations. Yet despite its widespread importance it remains an enigma and is surrounded by controversy. The Balance of Power traces the evolution of the theory from the eighteenth century to the present day. It incorporates classical anlysis and recent research to give a detailed account of the concept in practice and the operation of the international system while challenging traditional views of the balance of power. Its exploration of the way the balance of power operated in key historical periods shows how the generally accepted development of the concept is based on a misunderstanding of the historical reality.