This article analyses the diplomatic and financial efforts made by the ambassadors of Catholic and Protestant states to install, to maintain or to re-establish Orthodox prelates who were sympathetic to their respective causes at the Greek Patriarchate in Constantinople between 1620 and 1638. Cyril Lucaris (1572-1638) was the key figure during this twenty-year period. Supported by the English and Dutch ambassadors, this Greek prelate was appointed to the patriarchal seat five times, and deposed from the seat as many times, because of attacks against him by the ambassadors of the king of France and of the Emperor. Based on diplomatic correspondence from both sides and on a rich historiography, this investigation follows the changing attitudes of the rival parties, detects the repercussions of the confrontation in Constantinople on Central Europe and on the Holy Land, and reconstitutes, for the first time, a table of bids made by the Catholic and Protestant diplomats during the Thirty Years’ War which benefited the Ottoman Empire.