While contemporary Jews debate “Who is a Jew?”, medievals found the question “Who is not a Jew?” much more relevant. Halakhic standards were clear enough on entrance to the community: birth or conversion decided the matter, and the latter provided no more problems than did the average halakhic norm. The institution of conversion was not quite as old as that of birth, but it too had a respectable history of Talmudic discussion and stable international precedent behind it by the start of medieval times, and no Jewry found itself in a quandary on that score. This was not the case regarding Jews who rejected Judaism and left the community. Talmudic discussion is both sparse and incomplete on this issue; and it may not necessarily suit the case of the medieval apostate who exchanges his native fold for an equally possessive faith community. The medievals faced the problem, then, with some Talmudic guidelines but with many open options; yet despite the different opinions that developed, we are able to speak of a medieval concensus. This concensus delivered a legal standard, to be sure; but, as we might expect from an issue of such scope and centrality, the legal concensus was based on a broad understanding of the relation of the Jew to his people and the nature of Jewish peoplehood.