This book explores the diverse views of Gentile impurity found in Second Temple and raddinic sources. Christine Hayes seeks to determine the role such views played in the rise and development of sectarianism within late antique Jewish society and in the regulation of Jewish-Gentile others. Hayes discovers that different views on the question of Gentile impurity led to widely varying definitions of group identity and the permeability of group boundaries among the ancient Jews. These differing views of impurity resulted in widely divergent attitudes towards intermarriage and conversion - the two processes by which boundaries may be penetrated. She argues that different views of the possibility of conversion, based on differing ideas about impurity, were the key factors in the formation of Jewish sects in the second temple period, and in the separation of the early Christian Church from what would later be rabbinic Judaism.