ENOrthodox Jewry, a new phenomenon in modem Jewish history, took shape in Europe during the nineteenth century. Different variants emerged as a result of the prevailing temporal and local conditions. In its essence, Orthodoxy was the reaction of traditional Jewry to the challenges of modernity. This movement, which is one of the central manifestations of the period, expresses itself socially, ideologically and halachically. Its continuity, its endurance, its spiritual creativity and variety make it deserving of more attention than it has received to date. Research into Orthodox Judaism has recently progressed to the point at which we can make fine distinctions among related groups. We speak of: Orthodoxy, Neo-Orthodoxy, Ultra-Orthodoxy, Haredim, Religious Zionists, and Modem Orthodoxy; some of which originated in Western and Central Europe, others in Eastern Europe. Jacob Katz, Mordecai Breuer, Moshe Samet, Samuel Heilman, Steve Levinstaum, and others have already produced valuable research on the western and central European streams. By contrast, Eastern European Orthodoxy has remained virtually unexamined. I myself have done some work on religious Zionism, Israel Bartal on Orthodox historiography, Emanuel Etkes on the Musar movement, and Shaul Stampfer on the great Yeshivas of Eastern Europe. That about exhausts the field to date. In the past, I have always thought of Eastern European Orthodoxy as primarily a response to nationalism; therefore I dated its onset from the mid 1890's, when the growing resistance against the nationalist movements within the religious community led to the creation of Orthodox organizations.Although I did identify some earlier activity, I did not find it persistent enough or sufficiently organized to qualify as a social movement. Lately, however, some findings I have made about the late 60's and early 70's have caused me to change my mind. I now divide the development of Eastern European Orthodoxy into two stages: the ideological-theological and the Halachic. The controversy over religious reform which raged from 1868-1871 provided the keynote of the ideological phase, while the halachic phase emerged, between 1874 and 1878, within the context of the controversy about the ritual appropriateness of the etrogim (citrons) from Korfu, and a new compilation of talmudic material. In order to delineate the developing characteristics of early Orthodoxy in Eastern Europe, I will trace the progress of both the ideological and halachic debates [p. 104-105].