Philippe Buc's research has been concerned with religion and power in pre-modern western Europe, principally from Late Antiquity to the High Middle Ages, so the 2nd to 14th centuries of the Common Era. The geographic areas that he is most familiar with include what are now France, Germany, and the Low Countries, but given the translocal nature of political and religious elites in the Middle Ages, his space is by necessity the whole of Western Europe.