Yitzhak Isaac Halevy (Rabinowitz) (Hebrew: יצחק אייזיק הלוי; September 21, 1847 – May 15, 1914) was a rabbi, Jewish historian, and founder of the Agudath Israel organization.

A somewhat hagiographical treatment based on discovered correspondence of Isaac Halevy is to be found in Reichel (1969), and this forms the basis for the present article.

He held a number of communal positions in his early adulthood, including gabbai of the aforementioned Volozhin Yeshiva.

Halevy was influential in having R. Chaim Soloveichik appointed to head the yeshiva, and he hosted the latter in his own house for months at a time.

Although Halevy is best known for his classic work Dorot Harishonim, rebutting many of the mainstream historical accounts of Jewish history, he was also most influential behind the scenes in uniting the leading rabbis of the West and of the East in forming the Agudath Israel world movement, as described by Reichel.