On Judaism is a collection of lectures by Martin Buber that had a profound influence on European Judaism in the early 20th century. The most interesting parts of this book are the lectures Buber delivered between 1909 and 1918, whose achievement was to convince intellectuals once again to take seriously the mystical elements of Judaism, such as kaballah. Assimilationism, secularism, and materialist skepticism had convinced many European Jews that religious Judaism demanded mindless allegiance to outmoded laws--a situation, as Rodger Kamenetz notes in his introduction to this volume, that bears a striking resemblance to the mindset of many young Jews today. Buber"s involvement with Theodore Herzl"s Zionist movement (which led to the creation of the state of Israel) gave him credibility with Jewish intellectuals, however. He used this credibility to persuade his listeners that there is an essential difference between rigid, legalistic "religion" and the vital, world-engaging "religiosity" that, he contended, is the prevailing character of Torah. As Kamenetz writes, "Buber"s enduring insight is that Judaism is a process, not a conclusion: a religion of presence, and not simply an historical religion." Obviously, much has changed since Buber delivered these early lectures--the two World Wars, the Holocaust, and the rise of Reformed Judaism have forever altered the context in which young Jews define their religious identity. But Buber"s driving question--"I must ask myself again and again: Is this particular law addressed to me and rightly so?"--is still the most important one for Jews who seek to understand themselves as people of the book. Martin Buber asked that question with unremitting intensity and intellectual rigor, and On Judaism will help its readers to do so as well. --Michael Joseph Gross