During the course of the twelfth century, increasing numbers of Jews migrated into dynamically developing western Christendom from Islamic lands. The vitality that attracted them also presented a challenge: Christianity - from early in its history - had proclaimed itself heir to a failed Jewish community and thus the vitality of western Christendom was both appealing and threatening to the Jewish immigrants. Indeed, western Christendom was entering a phase of intense missionising activity, some of which was directed at the long-term Jewish residents of Europe and the Jewish newcomers. This study examines the techniques of persuasion adopted by the Jewish polemicists in order to reassure their Jewish readers of the truth of Judaism and the error of Christianity. At the very deepest level, these Jewish authors sketched out for their fellow Jews a comparative portrait of Christian and Jewish societies - the former powerful but irrational and morally debased, the latter the weak but reasonable and morally elevated - urging that the obvious and sensible choice was Judaism.