The aim of this thesis is to examine the role and the contribution of the economic and trade diplomacy in the United States of America, in China and in the European Union. In particular, the contribution of the economic and trade diplomacy in the evolution of the United States into a superpower, of China into a rapidly developing economy which seems to disturb the worldwide power correlation and of the European Union into a strong worldwide trade player will be examined. The importance of trade and trade negotiations in the early days of the United States until the most recent protectionist views of President Trump, the Belt and Road Initiative which can be seen as the New Silk Road for China and the development of the European Union from a group of six states into a total of twenty seven through a customs union, a single market and finally an economic and monetary union are presented. Greece is examined as a case study of a member state of the European Union, since it has regulated by law economic and trade diplomacy recently. A comparison of the economic and trade diplomacy in the United States of America, in China and in the European Union is made based on two factors; the role of the economic and trade diplomacy in the creation of them and the actors in each of them. The conclusion is that economic and trade diplomacy has contributed to the evolution of the USA into a superpower, of China into a rapidly developing economy which seems to disturb the worldwide power correlation and of the European Union into one of the biggest economies and a strong trade player worldwide. The contribution of this paper is the study of a subject not often examined, that is economic and trade diplomacy.