Zecharias Frankel (30 September 1801 – 13 February 1875) was a Bohemian-German rabbi and a historian who studied the historical development of Judaism. He was born in Prague and died in Breslau. He was the founder and the most eminent member of the school of positive-historical Judaism, which advocates freedom of research while upholding the authority of traditional Jewish belief and practice. This school of thought was the intellectual progenitor of Conservative Judaism and Neolog Judaism.

Through his father, he was a descendant of the Vienna exiles of 1670 and of the famous rabbinical Spira family; on his mother's side he descended from the Fischel family, which has given the community of Prague a number of distinguished Talmudists. He received his early Jewish education at the yeshiva of Bezalel Ronsburg (Daniel Rosenbaum). In 1825 he went to Budapest, where he prepared himself for the university, from which he graduated in 1831. In the following year he was appointed district rabbi (Kreisrabbiner) of Litoměřice by the government, being the first rabbi in Bohemia with a modern education. He made Teplice his seat, where the congregation, the largest in the district, had elected him rabbi. He was called to Dresden in 1836 as chief rabbi, and was confirmed in this position by the Saxon government. In 1843 he was invited to become the chief rabbi at Berlin, which position had been vacant since 1800. However, after a long correspondence he declined, chiefly because the Prussian government, in accordance with its fixed policy, refused to officially recognize the office. He remained in Dresden until 1854, when he was called to the presidency of the Breslau seminary, where he remained until his death.

Frankel held that reason based on scholarship, and not mere desire on the part of the laity, must be the justification for any reforms within Judaism. In this sense Frankel declared himself when the president of the Teplice congregation expressed the hope that the new rabbi would introduce reforms and do away with the "Missbräuche" (abuses). He stated that he knew of no abuses; and that if there were any, it was not at all the business of the laity to interfere in such matters (Brann, in his "Jahrbuch," 1899, pp. 109 et seq.).

He introduced some slight modifications in Jewish prayer services such as: the abrogation of some hymns, the introduction of a choir of boys, and the like. He was opposed to any innovation which was objectionable to Jewish sentiment. In this respect, his denunciation of the action of the "Landesrabbiner" Joseph Hoffmann of Saxe-Meiningen, who permitted Jewish high-school boys to write on the Sabbath, is very significant ("Orient," iii. 398 et seq.).

His position in the controversy on the new Hamburg prayer book (1842) displeased both parties; the liberals were dissatisfied because, instead of declaring that their prayer-book was in accord with Jewish tradition, he pointed out inconsistencies from the historical and dogmatic points of view; and the Orthodox were dissatisfied because he declared changes in the traditional ritual permissible (l.c. iii. 352–363, 377–384).

A great impression was produced by his letter of 18 July 1845, published in a Frankfurt-am-Main journal, in which he announced his secession from the rabbinical conference then in session in that city. He said that he could not cooperate with a body of rabbis who had passed a resolution declaring the Hebrew language unnecessary for public worship. This letter made Frankel one of the leaders of the conservative element. In opposition to the rabbinical conferences, he planned conventions of scholars. His principles were enunciated in his monthly Journal of the Religious Interests of Judaism, which he published from 1844 onward. But Frankel's conciliatory attitude was bound to create for him enemies on both liberal and orthodox sides, and such was the case with Abraham Geiger and Samson Raphael Hirsch, respectively.

Frankel was chosen president of the new rabbinical seminary at Breslau (10 August 1854). Geiger, who had inspired Jonas Fränkel, the president of his congregation, to found this institution, opposed the appointment vigorously, and when the examination questions given by Frankel to the first graduating class appeared, Geiger published them in a German translation with the evident intention of ridiculing his methods of Talmudic instruction as sophistry (Geiger, "Jüd. Zeit." i. 169 et seq.).

Samson Raphael Hirsch, immediately on the opening of the seminary, addressed an open letter to Frankel, demanding a statement as to the religious principles which would guide the instruction at the new institution. Frankel ignored the challenge. When the fourth volume of Heinrich Graetz's history appeared, Hirsch impeached the orthodoxy of the new institution (1856), and his attacks became more systematic when Frankel in 1859 published his Hebrew introduction to the Mishnah. The first attack began with the letter of Jedidiah Gottlieb Fischer [hu], rabbi of Székesfehérvár, published in Hirsch's "Jeschurun", 1860. Hirsch himself began in the following year a series of articles in which he took exception to some of Frankel's statements, especially to his definition of rabbinical tradition, which he found vague; he further objected to Frankel's conception of the rabbinical controversies, which were, according to Frankel, improperly decided by certain devices common in parliamentary bodies.