This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book focuses on the Holy Roman Empire, the heartland of the Reformation and, on account of its unique political structure, the site of some of the most interesting accommodations between governors and their subjects. It indicates the diverse directions in which Reformation scholarship is now moving, while reminding us of the need to understand particular developments within a broader European context. In Germany, the authority of Lutheran princes within their own territories may have been strengthened, but the ideological unity of the Holy Roman Empire was compromised, and collapsed entirely with the onset of the Thirty Years' War. England may not have had local Kirk sessions, but court act books and deposition books offer plenty of evidence of clergy and churchwardens providing informal justice, arbitration and conciliation.