Theology develops in debate, in lore on difficulties and conflict. In 18 articles the theologians of the 2nd to the 15th century are introduced. These have added decisively to solve imminent questions. After a biographical overview and placement in the historical context each author's position to his topic is laid out through the chief. Historical breaks from Nicaea to Nominalism frame the work and show the in depth theological knowledge. Thus a concentrated overview of the history of theology, that introduces, orientates and facilitates in depth studying, is given. The 16th to the 21st century is topic of the second volume.