For two centuries Jews have struggled with a dual challenge: how and why to remain Jewish in the modern world? The questions "how" and "why" be Jewish are not in themselves new. But for the modem Jew they have carried an urgency and an uncertainty greater than that which most of his ancestors experienced. The post-Emancipation, post-Enlightenment history of Jewry and Judaism is one of continuous reformulation of the meaning of being Jewish. The process of reformulation has been complex and often contentious. Its products-the diverse forms of Jewishness manifest today-constitute tenuously successful responses to the dual challenge of Jewish self-definition in the modem world. But the challenge itself persists and repeatedly thrusts itself forward. It is the fundamental Jewish reality of our time, the text, as it were, to which modern Jews are writing and rewriting ever new commentary.