Justification by faith alone defined teaching in Evangelical churches of the sixteenth century. When the former reformer of Nuremberg, Andreas Osiander (1498-1552) advocated a different understanding of that doctrine in 1550 as professor of theology at the University of Königsberg in East Prussia, almost all other Evangelical churches in German-speaking lands rejected his position. Timothy J. Wengert studies their objections to Osiander’s theology in detail, offering a theological perspective on the process of confessionalization among Lutherans in the period between Martin Luther’s death in 1546 and the publication of the Book of Concord in 1580. Reactions against Osiander represent a singular literary event, when 100 tracts for and against Osiander’s position were published between 1551 and 1559. The author of this study examines these responses, paying special attention to the contributions of Gnesio-Lutherans, Johannes Brenz and Philipp Melanchthon but also to the role that Luther’s writings played in the debate.