This study argues that the use of reflected self-image as a tool for interpreting Christian anti-Muslim polemic allows such texts to be read for the self-image of their authors instead of the image of just those they attacked. This self-image is further described as the author's assertion of Christian identity in light of Islam. As such, polemic becomes a set of boundaries authors offered to their communities, helping them to successfully navigate inter-religious living. Using this interpretive tool, two sets of medieval anti-Muslim polemic from Spain - four treatises from the third/ninth century and four from the fifth/eleventh-sixth/twelfth centuries - are analysed in order to discern how their authors defined themselves in light of Islam, and in turn, how they hoped their readers would distinguish themselves from Muslims. The research found differences in both the strategies deployed by the different sets of texts and the definitions of Christian identity that result from them. In the first case, Christian defamation of Islam is used to define Christians by their isolation from Muslims. In the second case, familiarity with Islam and Muslim culture reveals a definition of Christianity more supportive of the cultural proximity to Muslims even as Christians' religious distinctiveness is emphasised.