The first volume of Joachim Whaley's encyclopedic history of the Holy Roman Empire in early modern Europe covers its history from the start of the 16th century to the end of the Thirty Years' War. It's main theme is the impact of the Protestant Reformation upon the empire, which polarized it and ultimately led to one of the most destructive wars in European history. Yet Whaley shows that the polarization which caused so much conflict was only one dimension of what was a complex interaction. Just as the Reformation spread and developed under the protection of the legal protections provided by the complex institutions of the empire, the empire in turn was shaped by the political and legal struggles spawned by the Reformation, which encouraged the maintenance of the diverse political institutions in the face of efforts by the reigning Habsburg emperors to centralize power in their hands. Whaley's patient and thorough explanation of this intricate dynamic makes for a book that is indispensable reading for anyone interested in early modern Germany, or how the Reformation expanded and survived. ( )