Yitzchak Yaacov Reines (Hebrew: יצחק יעקב ריינס, Isaac Jacob Reines), (October 27, 1839 – August 20, 1915) was a Lithuanian Orthodox rabbi and the founder of the Mizrachi Religious Zionist Movement, one of the earliest movements of Religious Zionism, as well as a correspondent of Theodor Herzl.

Yitzchak Yaacov Reines, a descendant of Meir ben Isaac Katzenellenbogen,[1] was born in Karolin (now a part of Pinsk, Belarus).

Although the plan to supply Russian-speaking rabbis agreed in principle with the aims of the Russian government, there was so much Jewish opposition to his yeshivah that it was closed by the authorities after an existence of four years; all further attempts of Reines to reestablish it failed.

He was instrumental in the establishment of the first “kollel” perushim, for the purpose of subsidizing young married men studying for the rabbinate, under Rabbi Yitzchak Blazer.

At the fifth Zionist congress (1901 in Basel), the Swiss and radical student faction threatened to turn the movement in a direction which would lead away from religion.

In it, he made a call to a Zionist Judaism for all Jews, one that included economic productivity and training, and a renewal of Jewish thought, emotion, and action.

In 1905, Reines accomplished his own personal dream, with the establishment of a yeshiva in Lida where both secular and religious subjects were taught.