The present work is a contribution to the history of the Early modern diplomacy and early modern diplomatic practics. The subject of this work is the diplomatic misson of Baltasar de Zúñiga at imerial court (1608-1617). The study focuses on description of embassy functioning based on an analyses of official documents produced by the embassy itself, which were in several instances complemented by some of the documents produced by the Spanish governmental bureucracy such as, instructions, credentials, consultas or correspondence addressed to the hands of ambassador Baltasar de Zúñiga. As such, the present study is a kind of introspection, because it shows the functioning of a diplomatic mission from inside. The aim is to aswer the following questions. What part of the day-to-day work of a specific embassy could be seen, and controled by a sending government. How the chosen sources represent the basis of the Spanish policy in the Holy Roman Empire, the instruments used to increase the reputation of the Spanish king and the reputation of the ambassaror himself.