The crucial question for today's Jewish world, Menachem Kellner argues, is not whether Jews will have Jewish grandchildren, but how many different sorts of mutually exclusive Judaisms those grandchildren will face. Kellner's short, brisk, and accessible book examines how the split that threatens the Jewish future can be avoided. The first six chapters of this strongly argued book analyse what religious faith means in classical Judaism and will be of interest to anyone seeking lucid insights into the nature of Judaism. The final chapter builds upon the conclusions of the first six in order to argue for a new way of construing the relationship of Orthodoxy to non-Orthodox Jews and institutions. Kellner argues that the Orthodox practice of framing the debate with non-Orthodox movements in terms of dogmatic fidelity contrasted with heresy is not the traditional Jewish approach, and that the debate could well be framed in other ways, ways that would allow all Jews to work together towards a less polarized Jewish future. Undoubtedly, Must a Jew Believe Anything? has the potential to make a difference to how Orthodoxy understands itself and its relationship to other Jewish movements in the modern world. For the second edition, the author has added a substantial Afterword, reviewing his thinking on the subject and addressing the reactions to the original edition.