Protestantism and Islam entered into contact during the 16th century, at a time when Protestant movements in northern Europe coincided with the expansion of the Ottoman Empire in southern Europe. As both were in conflict with the Catholic Holy Roman Empire, numerous exchanges occurred, exploring religious similarities and the possibility of trade and military alliances.
Relations became more conflictual in the early modern and modern periods, although recent attempts have been made at rapprochement. In terms of comparative religion, there also interesting similarities, as well as differences, in both religious approaches.
The Sultan of the Ottoman Empire was known for his tolerance of the Christian and Jewish faiths within his dominions, whereas the King of Spain did not tolerate the Protestant faith.
The Ottoman Empire was indeed known at that time for its religious tolerance. Various religious refugees, such as the Huguenots, some Anglicans, Quakers, Anabaptists or even Jesuits or Capuchins were able to find refuge at Istanbul and in the Ottoman Empire, where they were given right of residence and worship. Further, the Ottomans supported the Calvinists in Transylvania and Hungary but also in France. The contemporary French thinker Jean Bodin wrote:
"The great emperor of the Turks does with as great devotion as any prince in the world honour and observe the religion by him received from his ancestors, and yet detests he not the strange religions of others; but on the contrary permits every man to live according to his conscience: yes, and that more is, near unto his palace at Pera, suffers four diverse religions viz. that of the Jews, that of the Christians, that of the Grecians, and that of the Mahometans"
Martin Luther, in his 1528 pamphlet, On War against the Turk, calls for the Germans to resist the Ottoman invasion of Europe, as the catastrophic Siege of Vienna was lurking, but expressed views of Islam which, compared with his virulent anti-Semitism, are relatively mild. On the one hand, Luther extensively criticized the principles of Islam; on the other hand, he also expressed tolerance for the Islamic faith:
"Let the Turk believe and live as he will, just as one lets the papacy and other false Christians live."
—Excerpt from On war against the Turk, 1529.
However, this statement mentions "Turks", and it is not clear whether the meaning was of "Turks" as a representation of the specific rule of the Ottoman empire, or as a representation of of Islam in general.
Martin Luther's ambivalence also appears in one of his other comments, in which he said that "A smart Turk makes a better ruler than a dumb Christian".