Book excerpt: Denise Kimber Buell radically rethinks the origins of Christian identity, arguing that race and ethnicity played a central role in early Christian theology. Focusing on texts written before the legalization of Christianity in 313 C.E., including Greek apologetic treatises, martyr narratives, and works by Clement of Alexandria, Origen, Justin Martyr, and Tertullian, Buell shows how philosophers and theologians defined Christians as a distinct group within the Roman world, characterizing Christianness as something both fixed in its essence and fluid in its acquisition through conversion. Buell demonstrates how this view allowed Christians to establish boundaries around the meaning of Christianness and to develop the kind of universalizing claims aimed at uniting all members of the faith. Her arguments challenge generations of scholars who have refused to acknowledge ethnic reasoning in early Christian discourses. They also provide crucial insight into the historical legacy of Christian anti-Semitism and contemporary issues of race.