The Ambassadors, as actors of diplomatic contacts between the Islamic East, the West and the Christian East in the second part of the Middle Ages, are at the heart of this book. It brings together various contributions from researchers and historians working on the history of medieval diplomacy. It is the written version of a study day organised in June 2012 as part of the Scientific Days of the University of Nantes. This international meeting was the result of a partnership between several institutions (CRHIA, University of Nantes, Practical School of Advanced Studies, University of Liège and CNRS, UMR 8167 “East and Mediterranean”) taking part in one of the themes of the IFAO (Institut Français d’Archéologie Orientale — Cairo) programme “La Paix: concepts, practices and political systems”. In the articles grouped together here, the authors answer common questions, albeit each of them on their own survey areas. What is an ambassador between the spaces and civilisations under consideration and for the period taken into account? Is this concept, at the risk of anachronism, really compatible with the functions of spokesman and official representation held by these men? How does the terminology of the multiple sources in various languages (Latin, Greek, Arabic, Armenian, old Slavon, etc.) the historian has defined these intermediaries between states, princes or sovereign political entities? What are the specific features of these ambassadors circulating over large distances between neighbouring but often rival civilisations? These are all legitimate questions to which the contributions give some answers, providing new avenues for reflection and allowing for suggestive comparisons, although not intended to be exhaustive. The reader will thus be able to understand the activity of some of these official envoys in spaces as diverse as the shores of the Indian Ocean, the main political and economic centres in the medieval Mediterranean (Constantinople, Cairo, Pisa, Venice, etc.), the Romanian and Armenian principals, or follow the routes of pontifical envoys to the 18th century East.