This book is a highly informed and meticulously researched historical study of western European left Catholic thinkers writing and working during the first half of the twentieth century. They may be styled as thinkers of the ‘left’ because they were concerned with rejuvenating Catholic theology in the wake of the Modernist crisis, as well as with ensuring that their religious commitments effected political changes in their respective countries so as to redress the social vulnerability and economic wretchedness of masses of working-class people. Prominent among these thinkers and activists was the Belgian priest, Joseph Cardijn, and among the French, the social activist and intellectual Emmanuel Mournier, the Dominican theologian Marie-Dominique Chenu, and the philosopher and eventual French ambassador to the Vatican, Jacques Maritain. The book also draws attention very creatively and instructively to the work of two Italian priests, Don Primo Mazzolari and Don Zeno Saltini. The historical compass of the book includes the creation in 1924 of two organisations for young Christian workers – the Flemish group, Kristene Arbeidersjeugd, and its francophone analogue, Jeunesse Ouvrière Chrétienne, and the eve of the Second Vatican Council (1959). A prominent feature of the book is the way it traces the evolution of Catholic Action in western Europe, and theologies of labour and lay participation in ecclesial life. The text focuses primarily on thinkers in France, Belgium and Italy. One minor quibble: the Syllabus Errorum of 1864 was not, strictly speaking, a papal encyclical, but a list of theses that was attached to the encyclical Quanta Cura. The reader of this book needs to be alert to what it actually expounds. The title has the potential to be misleading. The term ‘liberation theology’ was coined in the late 1960s in South America. One of the first recognisable expositions of this type of theology was a series of lectures delivered by Juan Luis Segundo in Montevideo during 1959, and was developed in an embryonic phase most notably by Gustavo Gutiérrez from 1968 to 1972. Liberation theology is like any other type of theology in that it is discourse about God. Its distinctive feature in its South American form is its method – a critical reflection on praxis undertaken in view of the Bible. By ‘liberation theology’, Gerd-Rainer Horn means a form of ‘progressive Catholicism’ or ‘Left Catholicism’ (both his expressions) in Europe, which he takes to be a prototype for the liberation theologies that emerged in South America during the second half of the twentieth century. The primary intellectual lodestar of this type of Catholicism, which had not been crushed by anti-Modernist practices, was Jacques Maritain. Yet Maritain's doctrine of a separation between spiritual and temporal spheres would be deeply inimical to many liberation theologians. It is no accident that Horn is at pains to justify his title (pp. 291–301), because he is fully aware that it is ‘somewhat controversial’ (p. 3). Horn is correct in arguing that there is no logical reason why the term ‘liberation theology’ ought to be confined to its South American practitioners, but the European authors he presents (such as Maritain and Chenu) did not regard themselves as liberation theologians as these are now most commonly understood. They did not advocate an epistemological priority of orthopraxis over orthodoxy, or live exclusively among the wretchedly poor. What the book actually provides is an analysis of European social action groups and reform-minded Catholic intellectuals concerned that Christian faith should have practical, political effect to empower lay people and help poor people. A less potentially ambiguous title is suggested by the author himself when he describes his volume in terms of a study of ‘the first wave of left Catholics’ (p. 175). Horn's is an important and welcome voice among historians because he writes in the era of Popes John Paul ii and Benedict xvi, when progressive, radical or liberal theological and historical voices have been known to be muted or dismissed. Horn's book admirably brings into sharp relief the progressive Catholicism that emerged in Europe in the wake of the Modernist crisis and the First World War, and illustrates that anti-Modernist strictures were not ultimately triumphant among European Catholics.