The four volumes or sections comprising Beit Yosef, undoubtedly one of the fundamental books in the history of the Halakhah, were printed between 1550 and 1559. Its importance was demonstrated by the enthusiastic welcome the work received shortly after its publication and by its impact in the long run. For three centuries, the long code of law attracted important commentaries by the leading Talmudic scholars around the Mediterranean Basin and in Eastern and Central Europe (mainly in Poland); later, it even inspired the composition of commentaries on previous codes authored by Maimonides (Mishneh Torah) and R. Jacob ben Ha-Rosh (Ha-Turim or Arbaʽa Turim). The most impressive fact of all, however, is that along with the glosses of the contemporary Polish rabbi Moses Isserles on the short version of this magnum opus—the Shulchan ʽArukh—Karo's work has not to the present day been succeeded by any further code of law. The importance of both these codifications was acknowledged by their composer R. Joseph Karo in fascinating preambles, declaring that Jewish tradition is constituted through legality and halakhic instruction rather than through any other component of Jewish heritage. This was a watershed moment in the history of Jewish culture and religion, and one that prepared ground for the later crystallization of Orthodox Judaism and the contemporary ultra-Orthodox worldview and community life. Law and Halakhah were interconnected with Jewish mystic tradition—Kabbalah—and with new theological conceptions. Together these three elements provided the early modern rabbinical elite with the essential tools to reform and revitalize Jewish tradition.

What was the starting point for the composition of Beit Yosef, and later the Shulchan ʽArukh, which turned R. Karo into a Talmudic celebrity? How far back should we go in order to understand what stood behind these magna opera? The first time axis is certainly the biographical trajectory of the composer himself, and especially the scholarly path that he followed as a member of a rabbinical family and the scholarly milieu. This extremely small elite assigned the most talented among the young generation to become a Talmudic scholar (talmid chakham), rabbi, judge, or even a halakhic arbiter (poseq), at the peak of the rabbinical hierarchy. Little is known of the early phases of Karo's initiation into rabbinical scholarship, except for the fact that his uncle R. Isaac Karo was his first and probably most significant master.