This is a pioneer theoretical study of diplomacy from the viewpoint of political science. It defines diplomacy precisely, and distinguishes it from the other institutions with which it is often confused. The work commences with a historical analysis of diplomacy through the ages in order to afford a theoretical description of the concept. After defining the term, Calvet de Magalhaes goes on to examine the value of current ideas concerning diplomacy. He also describes deviations from normal diplomatic practice, such as backchannel diplomacy, combat diplomacy, and espionage. The work concludes with a detailed precis of the different elements of diplomatic activity.