R. Israel Hildesheimer (Azriel) (1820–1899) was a German rabbi, scholar, educator, and leader of Orthodox Jewry. R. Hildesheimer was born in Halberstadt, and received his early education in the local Jewish school, the first in Germany to include general subjects in its curriculum. He continued his talmudic studies under Jacob Ettlinger in Altona, and attended the lectures of Isaac Bernays in neighboring Hamburg. At Berlin University he studied Semitics, philosophy, history, and science, and eventually received his doctorate from the University of Halle. His dissertation, "The Correct Method of Interpreting the Bible," dealt with the Septuagint. By his marriage to the daughter of Aaron Hirsch he became financially independent, enabling him to pursue freely his university studies and his subsequent career. On his return to Halberstadt, Hildesheimer assumed the voluntary post of secretary to the community.

In 1851 Hildesheimer was appointed rabbi of Eisenstadt; where he reorganized the educational system and established a yeshivah, where secular studies were included in the curriculum. Many of the courses were taught by Hildesheimer himself. The yeshivah was highly successful. Despite Hildesheimer's great learning and patent Orthodoxy, the great majority of Orthodox Hungarian rabbis bitterly opposed his modernism and the institution he created. At a congress of Hungarian Jewry in 1868–69, which met to decide on the establishment of a rabbinical seminary for the whole of Hungary, Hildesheimer and his sympathizers had to contend with both the Reform and the ultra-Orthodox factions. His moderate proposals might have preserved the unity of Hungarian Jewry, but the congress ended in a radical split.

Despairing of success in Hungary, in 1869 he accepted a call from Berlin to become rabbi of the newly founded Orthodox Adass Jisroel. In 1873 he established a rabbinical seminary which later became the central institution for the training of Orthodox rabbis in Europe. R. Hildesheimer's students carried with them all over the world the notion that their Orthodoxy was compatible with scientific study of Jewish sources. R. Hildesheimer counseled close cooperation between all bodies in the community for the sake of the Jewish people as a whole. He believed such cooperation to be particularly important in the battle against German anti-Semitism in which he participated together with his Reform colleagues. At the same time he vigorously opposed the Reform movement throughout the course of his career as a force undermining the faith of Judaism.

R. Hildesheimer was an active worker on behalf of stricken Jewish communities throughout the world. He was alone in pleading that the survivors of the Russian pogroms be directed to Erez Israel instead of the New World. Throughout his life, he was an enthusiastic supporter of Palestine Jewry and the building of the yishuv. In Eisenstadt he had collected large sums for Jerusalem Jewry. The Battei Mahaseh dwellings in the Old City of Jerusalem were erected on his initiative. In 1872 he founded a Palaestina Verein with the object of raising the educational and vocational standards of Jerusalem Jews, particularly by the establishment in 1879 of an orphanage. This drew on his head the bitter antagonism of the ultra-Orthodox old yishuv, which placed him under a ban (herem). Hildesheimer supported the Hovevei Zion and the colonization movement; he was in particularly close contact with R. Zevi Hirsch Kalischer. For politico-legal reasons the newly acquired lands of Gederah were registered in his name; his excellent relations with the German Foreign Office were of value in securing its support for the yishuv.

R. Hildesheimer contributed regularly to German-Jewish periodicals. In 1870 he founded in Berlin the Juedische Presse, which was later edited by his son Hirsch. This paper was the only one in Germany at that time to give unequivocal support to the emigration of German Jews and their settlement in Palestine. Though Hildesheimer's energies were severely taxed by his labors on behalf of the community, his contributions to Jewish scholarship were by no means insignificant. Of particular importance is his edition of Halakhot Gedolot from a Vatican manuscript (1888–90), which represented a hitherto unknown version of this important gaonic work. He also published some smaller studies in rabbinics, generally as supplements to the annual reports of the rabbinical seminary. His responsa on the first two parts of the Shulhan Arukh appeared in 1969.