outstanding spiritual leader of Spanish Jewry of his time (known as El Rab de España 【the Rabbi of Spain】); he is remembered partly for his controversial decree of 1305 threatening to excommunicate all Jews less than 25 years old (except medical students) who studied philosophy or science.

As a leading scholar of the Talmud, the rabbinical compendium of law, lore, and commentary, Adret received inquiries on Jewish law from all over Europe, and more than 3,000 of his responsa (replies) still remain. Besides providing cultural data on Adret's time, his responsa strongly influenced the later development of authoritative codes of Jewish law, such as the Shulḥan ʿarukh (“The Well-Laid Table”) of the codifier Joseph Karo (1488–1575). Adret's many other writings include commentaries on the Talmud and polemics defending it against attacks by non-Jews.

Late in life, Adret became embroiled in a quarrel between the followers of the medieval Jewish philosopher Maimonides (Maimonides, Moses) and the members of a conservative, antirationalist movement led by a zealot known as Astruc of Lunel, who believed that the followers of Maimonides were undermining the Jewish faith by, for example, interpreting the Bible allegorically. It was Astruc who induced Adret to issue his famous decree against the study of philosophy and science. Although the ban itself did not bring about an end to such studies, it precipitated among Jews in Spain and southern France a bitter controversy that continued during Adret's last years.