The Peace of Passau was an attempt to resolve religious tensions in the Holy Roman Empire.
After Emperor Charles V won a victory against Protestant forces in the Schmalkaldic War of 1547, he implemented the Augsburg Interim, which largely reaffirmed Roman Catholic beliefs.
This angered many Protestant princes, and led by Maurice of Saxony, in January 1552 several formed an alliance with Henry II of France in the Treaty of Chambord.
In the ensuing Princes' Revolt, also known as the Second Schmalkaldic War, Charles was driven out of Germany to his ancestral lands in Austria by the Protestant alliance, while Henry captured the three Rhine Bishoprics of Metz, Verdun and Toul.
The Protestant princes taken prisoner during the Schmalkaldic War, John Frederick of Saxony and Philip of Hesse, were released.