Although in recent years there have been several studies which have examined the failure or delay of Reforming endeavour in German cities, this work, refreshingly modest in length and accessibly written, fills a two-fold gap. It presents the slow and contested introduction of evangelical doctrines in Frankfurt-am-Main, a city on which there is little literature in English; but it does so from an unusual perspective, namely that of a Catholic collegiate priest, Wolfgang Königstein, who recorded, with mounting alarm, the spread of Reforming doctrines among the citizenry at large, flanked by the council's efforts to put a brake on the movement on account of the constitutional and commercial privileges which the city derived from the emperor. What Moger is able to show is that the final acceptance of Reform in 1533, cemented by the city's joining the Schmalkaldic League three years later, wrought very few changes in the social and political fabric of the city. Rather, the fundamental shift was cultural and mental: the practices and rituals of Catholicism were sloughed off (with notably little physical violence, but with symbolic acts of iconoclasm) and replaced by a simplified liturgy and order of worship, visible above all in the recasting of baptism and holy communion, and the disappearance of processions. Königstein recorded these changes accurately (if despairingly); his only blind spot was the presence of a sizeable contingent of Reformed Protestants in the city, led by Dionysius Melander, whom he lumps together as ‘Lutherans’, even though Luther himself was moved to compose his Letter to those at Frankfurt am Main in late 1532 in order to counteract the acceptance of doctrines of Zwinglian or Bucerian provenance in the city. Königstein survived; he was not expelled, but chose to remain in a city from which he must have felt increasingly estranged; after 1548 Frankfurt became a community which officially tolerated a Catholic minority. His account (whether one calls it a diary or a chronicle) gives a running commentary on the gradual changes in ritual and belief, which Moger sensitively sets in context: he emphasises that, while we may never know why men and women chose to embrace or reject Protestantism, we can learn a great deal from what they did. Indeed, Moger's book may prove particularly useful beyond its immediate status as a case study, inasmuch as he gives careful explanations of, for instance, the structure and purpose of collegiate churches, or the practice and symbolism of Catholic baptism, matters with which students today are often unfamiliar.