Between the sixteenth and seventeenth centuries, the figure of the ambassador underwent profound changes. This volume investigates its various aspects, analysing the criteria for choosing the diplomat, the arrival and the long years spent at the host court, as well as the conditions of the return home. In the context of the significant growth of circulating information, the procedures for creating embassy archives are also considered. Attention is paid to the networks of relations, influenced by polycentrism in the decision-making processes, to the cultural implications, connected to the forms of diplomatic sociability, to the rapid and sometimes frenetic turnover of individuals entrusted with portions of diplomatic agency: secretaries, agents, men of letters, sometimes women. By offering an innovative analysis of the relationship between diplomatic treatises, forms of the political and practical sources on the ambassador, this volume critically reflects on some pivotal themes in the history of European diplomacy in the sixteenth and seventeenth centuries.