Pp. xxv, 290 , Washington DC , Catholic University of America Press , 2006 , $39.95. The twelfth century was pivotal in the history of Christian-Jewish relations in western Europe. A spreading tide of Christian violence against Jews started with pogroms in Rhineland cities during the First Crusade in 1096. Subsequent atrocities included in 1144 the case of St William of Norwich, and the invention of the libel that Jews murdered Christian children. The physical attacks were paralleled by a developing intellectual assault, as Christian writers produced a series of tracts framed as dialogues between advocates of the two religions, but intended to prove the superiority of faith of the New Testament over that of the Old. One of the most potent of these works was composed about 1109 in Spain by ‘Petrus Alfonsi’, a Jew who had converted to Christianity (like so many of those who wrote and acted most forcefully against Judaism in the medieval period). Engaging the two personalities of his old and new self, in a dialogue between ‘Moses’ and ‘Petrus’, he undertakes a strong defence of his new religion and the validity of his conversion against an admittedly weak opponent. The lengthy tract is split into twelve ‘tituli’, some of them focussed on criticism of the Jews, others dealing with specific Christian doctrines which have to be defended from Jewish attack, or used to demonstrate that Judaism had been supplanted. While the tract is supposedly aimed at Jews, at times it might more realistically be seen as an attempt to convince Christians of the validity of their faith in a time of controversy – and possibly a time of contest with a strong and assertive Judaism, one not averse to producing its own anti-Christian polemic. Given its purpose, Alfonsi's tract necessarily uses the Old Testament as its main foundation to demonstrate that Christ, and Christianity, is the successor to a religion now lacking any raison d'etre. The Old Testament is mined for foreshadowings of Christ, and predictions which his incarnation and ministry had fulfilled. As a converted Jew, it is not surprising that Alfonsi should have - or proclaim - some knowledge of Hebrew. This is invoked intermittently throughout his text, perhaps most notably (but how effectively only a Hebraicist could judge) when dealing with the crux of Isaiah's precise meaning in his prophecy of the Virgin Birth. ‘Moses’ may be a weak interlocutor, but he is not totally without verbal weapons. As the questioner, he ostensibly has the upper hand, and at times does push his opponent hard – in the process providing the impetus for an even stronger rebuttal. It is scarcely surprising that he eventually admits defeat. Alfonsi has to justify Christianity against Judaism, but he must also justify himself, and his choice of Christianity to replace his former faith. Not unreasonably, ‘Moses’ asks why Christianity was preferred to Islam. Alfonsi dedicates the whole of his fifth titulus (pp.146–63) to a reply. Although he certainly denigrates Islam, he purports to act on evidence rather than mere prejudice. Unlike the caricature of Islam presented, for example, in the Song of Roland, Alfonsi's Islam is firmly textual, with the Koran being cited against itself. Alfonsi wrote his text in Latin. He knew Hebrew and maybe Arabic (given his use of the Koran); knowledge of one or more of the vernacular Spanish languages can perhaps be assumed. His engagement in an Iberia of three religions and many languages underlines a work which became a mainstay of anti-Jewish polemic in later Christian Europe, feeding into the debates until the sixteenth century. Resnick's English translation, offered as volume 8 of the Fathers of the Church Mediaeval Continuation Series, provides a clear and accessible text, usefully annotated. His introduction gives a clear summary of scholarly debates about Alfonsi's work and its transmission, and identifies its place in the Jewish-Christian controversies of the twelfth century and later. While likely to be used mainly as evidence for inter-faith relations in the twelfth century, Alfonsi's Dialogue need not be so narrowly read. It also provides valuable evidence for other contemporary intellectual concerns, in the early days of scholastic theology. Its discussions of some issues (such as the process of creation) resonate with academic debates in the contemporary schools, and the emergence of the new theological science. Its long excursus (in the first titulus) on the location of ‘west’ and ‘east’, firmly shows that medieval scientists were fully aware that the earth was not flat. With its many facets, this is a text whose availability in English must surely be welcomed.