Schmalkaldic League in the context of Smalcald Articles

The Peace of Augsburg (German: Augsburger Frieden), also called the Augsburg Settlement, was a treaty between Charles V, Holy Roman Emperor, and the Schmalkaldic League, signed on 25 September 1555 in the German city of Augsburg. It officially ended the religious struggle between the two groups and made the legal division of Christianity permanent within the Holy Roman Empire, allowing rulers to choose either Lutheranism or Roman Catholicism as the official confession of their state. Calvinism was not allowed until the Peace of Westphalia.

The Peace of Augsburg has been described as "the first step on the road toward a European system of sovereign states." The system, created on the basis of the Augsburg Peace, collapsed at the beginning of the 17th century, which was one of the reasons for the Thirty Years' War.

The diets of Augsburg were the meetings of the Imperial Diet of the Holy Roman Empire held in the German city of Augsburg. Both an Imperial City and the residence of the Augsburg prince-bishops, the town had hosted the Estates in many such sessions since the 10th century. In 1282, the diet of Augsburg assigned the control of Austria to the House of Habsburg. In the 16th century, twelve of thirty-five imperial diets were held in Augsburg, a result of the close financial relationship between the Augsburg-based banking families such as the Fugger and the reigning Habsburg emperors, particularly Maximilian I and his grandson Charles V. Nevertheless, the meetings of 1518, 1530, 1547/48 and 1555, during the Reformation and the ensuing religious war between the Catholic emperor and the Protestant Schmalkaldic League, are especially noteworthy. With the Peace of Augsburg, the cuius regio, eius religio principle let each prince decide the religion of his subjects and inhabitants who chose not to conform could leave.

The Apology of the Augsburg Confession (German: Apologie des Augsburger Bekenntnisses) was written by Philipp Melanchthon during and after the 1530 Diet of Augsburg as a response to the Pontifical Confutation of the Augsburg Confession, Charles V's commissioned official Roman Catholic response to the Lutheran Augsburg Confession of 25 June 1530. It was intended to be a defense of the Augsburg Confession and a refutation of the Confutation. It was signed as a confession of faith by leading Lutheran magnates and clergy at the meeting of the Smalkaldic League in February, 1537, and subsequently included in the German [1580] and Latin [1584] Book of Concord. As the longest document in the Book of Concord it offers the most detailed Lutheran response to the Roman Catholicism of that day as well as an extensive Lutheran exposition of the doctrine of Justification.