Jacob Katz (Hebrew: יעקב כ"ץ) (born 15 November 1904 in Magyargencs, Hungary, died 20 May 1998 in Israel) was a Jewish historian and educator. He established the history curriculum used in Israel's High Schools.
Katz described "traditional society" and deployed sociological methods in his study of Jewish communities, with special attention to changes in halakhah (Jewish law) and Orthodoxy. He pioneered the modern study of Orthodoxy and its formation in reaction to Reform Judaism.
In the year 1945 Jacob Katz presented to a conference of historians his article “Marriage and Sexual Relations at the close of the Middle Ages” which was published that year in the periodical "Zion." Katz, who lived at that time in Tel Aviv and worked as a lecturer in a College of Education, had already been credited with a few articles in the fields of education, psychology and pedagogy, and their publication had given him a good reputation in the field. However, this reputation alone did not make him happy—he even suspected that it might distance him from the thing that he craved most of all, to get back to engagement in history research. It was Ben-Zion Dinur who encouraged Katz not to give up on his research even in the absence of an academic post. Indeed, despite the difficulty of setting aside time for research, Katz succeeded in completing the article mentioned. Its publication in the pages of Zion gave rise to favourable responses, and even won for Katz an invitation to participate in the first International Congress of Jewish studies which took place in Jerusalem in 1947. With hindsight it is possible to claim, that the article on “Marriage and Sexual Relations” in Zion paved the way for the integration of Katz into the Hebrew University. At the approach of the academic year 1949-1950, the University invited Katz to serve as an external teacher, offering him 25% of a full-time post.