Isaac Breuer (1883–1946) (Hebrew: יצחק ברויאר) was a rabbi in the German Neo-Orthodoxy movement of his maternal grandfather Samson Raphael Hirsch, and was the first president of Poalei Agudat Yisrael.
Breuer was born in Pápa, Austria-Hungary to Salomon Breuer, and lived most of his years in Frankfurt. His brother was Rabbi Joseph Breuer. He attended Hirsch's Realschule school, and received rabbinical ordination at age 20 from his own father's yeshivah. He studied law, jurisprudence, and philosophy at Marburg University, and until 1936 practiced law in Frankfurt.
In 1936 Breuer moved to Jerusalem, organized and became first president of Poalei Agudat Yisrael, and represented the Agudah before the Peel and Anglo American Commissions. He believed that Agudism could help prepare Jews to live in their ancestral home. (See below on his Zionism as a form of Agudah.) His five adult children were: Jacob (Bub) Baror, a lawyer who played a role in the Eichmann trial (1915–2008), Mordechai (1917–2007), Ursula (1919–2006, married Hermann Merkin), Tzipora (Tzip) Breuer Schneller (born 1926) and Simeon Breuer (1922–1943). His son-in-law Hermann Merkin helped to establish the Isaac Breuer College of Hebraic Studies (IBC program) at Yeshiva University in his memory.
Although Hirsch's neo-Orthodoxy movement had defined itself from the start largely as an opposition to the German Reform movement, Isaac Breuer already regarded the Reform movement of his day as essentially the impotent and dying remnant of the Haskalah (Biemann 2000). Breuer saw the real enemy of Orthodoxy in both political Zionism and Religious Zionism, which he considered especially dangerous because it possessed an authentic Jewish instinct and impulse. The goals of the Zionists paralleled the goals of his own Agudah organization in many areas ("reunification of land and nation"), but without the stress which Agudah laid on adherence to halachah and tradition (Biemann 2000). Indeed, Breuer envisioned a Messianic Torah state in the land of Israel, and could not abide the idea of "reunification of land and nation" coming to pass through the agency of secular Zionist forces in the form of a secular state.
- Judenproblem (1918), a polemic against the perceived opponents of Orthodoxy, Zionists and Reform Jews.
- Messiasspuren (1918)
- Concepts of Judaism Levinger, Jacob S. (ed.)
- Der Neue Kusari (Translated into Hebrew by his son Professor Mordechai Breur as Hakuzari Hachadash
- Jerusalem: eine historische Erzählung, a metaphor in novella form of what negative consequences might follow from the agenda of Zionists
- Mein Weg (1927)
- Biemann, Asher D. (2000), "Isaac Breuer: Zionist against his will?", Modern Judaism 20 (2): 129–146, doi:10.1093/mj/20.2.129.
- David N. Myers. Resisting History: Historicism and Its Discontents in German-Jewish Thought. Jews, Christians, and Muslims from the Ancient to the Modern World Series. Princeton and Oxford: Princeton University Press, 2003
- Alan L. Mittleman, Between Kant and Kabbalah: An Introduction to Isaac Breuer’s Philosophy of Judaism (SUNY, 1990)
- Alan Mittleman, Two Orthodox Jewish Theories of Rights: Sol Roth and Isaac Breuer - Jewish Political Studies Review Volume 3, Numbers 3-4 (Fall 5752/1991)
- Matthias Morgenstern, From Frankfurt to Jerusalem Isaac Breuer and the History of the Secession Dispute in Modern Jewish Orthodoxy
- Matthias Morgenstern Von Frankfurt nach Jerusalem: Isaac Breuer und die Geschichte des `Austrittsstreits' in der deutsch-jüdischen Orthodoxie Reviewer: Marc B. Shapiro in Journal of Jewish Studies Volume 48, Issue 2, Autumn 1997
- Meir Seidler, "Isaac Breuer's Concept of Law" Jewish Law Association Studies VIII The Jerusalem 1994 Conference Volume
- George Y. Kohler, "Is there a God an sich? Isaac Breuer on Kant’s Noumena", in: AJS Review 36:1 (2012), p. 121-139.
- Isaac Breuer's political philosophy (English)
- Biography of Isaac Breuer in German
- Breuer on the meaning of the Passover Seder
- Breuer on Yom Kippur
- Eulogy by his granddaughter for his daughter Ursula Merkin- contains comments on Breuer's life
- Isaac Breuer College of Hebraic Studies (IBC), Yeshiva University