Beda Mayr (1742–94) was a Benedictine monk of the abbey of the Holy Cross in Donauwörth. He was one of the most prominent monastic representatives of the Catholic Enlightenment in Germany. This well-edited volume reproduces the third book of Mayr's ‘defence’ of ‘natural, Christian and Catholic religion’, along with his appendix laying out the ‘possibilities for a reunion between’ the Catholic and Lutheran Churches. The great worth of this volume is that it will make accessible to a wide variety of readers a key text from the later phase of the German Catholic Enlightenment, and contribute to a general rediscovery of the complex ways in which Enlightenment reforms, cross-confessional discussion and ecumenical theology interacted with each other in the final decades of the Holy Roman Empire. Many will of course be surprised to learn that there was such a thing as a ‘monastic Enlightenment’. As Mayr himself writes, ‘people never imagine anything reasonable to come from monks, and judge them only by the size of their bellies, the cut of their gowns, and their shaved heads’ (p. 3). Ulrich L. Lehner's lengthy introduction on ‘Ecumenism and Enlightenment Catholicism’ offers a substantive and thorough presentation of current research on the place of monks and monastic culture in the Catholic Enlightenment in Germany, accompanied by a detailed scholarly apparatus and bibliography. He shows how Benedictines, in particular, built on a culture of erudition and historical scholarship to participate in a broad moderate religious Enlightenment. Lehner demonstrates how religious thinkers such as Mayr felt a need to confront the rise of radical Deism, and thought that Enlightened Catholics could make common front with Protestants against unbelief and superstition alike. Lehner notes that the third volume of Mayr's Vertheidigung ‘can be considered a new Summa of Catholic apologetics, since it not only presents a summary of what philosophy, theology, and science of religion have produced in the seventeenth and eighteenth centuries, but also presents a clear analysis of what value these new ideas have for Catholic theology’ (p. xxvi). Mayr's book is a theological text, and readers unfamiliar with eighteenth-century religious reform movements will not necessarily recognise it as an ‘Enlightenment’ text. But for Mayr, like most of his Catholic Enlightenment brethren, true religion and the progress of reason went hand-in-hand. It is to Lehner's great credit that scholars and students of the religious Enlightenment now have ready access to one of its exemplary texts.