Isaac Leeser (December 12, 1806 – February 1, 1868) was an American Orthodox Jewish religious leader, teacher, scholar and publisher.

In 1828, Leeser published a letter in the Richmond Whig which used Jewish history to respond to an anti-Semitic article in the London Quarterly.

Six years later, he discussed his rationale in a letter to Rabbi Solomon Hirschell of London: "Knowing my own want of proper qualification, I would never have consented to serve, if others more fitting in point of standing, information, or other qualities had been here; but this not being the case (as is proved by there being yet two congregations at least in this country without a regular hazzan), I consented to serve."

Gershom Mendes Seixas, the synagogue's first rabbi and congregation founder had delivered sermons in English on occasion, as had Rev.

Preaching in German soon became the norm in Reform synagogues, and even some conservative rabbis, such as Isaac Bernays, had begun to deliver sermons in the vernacular.

Leeser's practice of delivering sermons on a regular basis was ultimately adopted by American congregations, and preaching became one of the standard duties of Jewish clergymen.

[6] Three years later, Leeser published a Masoretic Hebrew edition of the Tanakh, Biblia Hebraica, in cooperation with Joseph Jaquett, a local Episcopalian minister.

Many Jews emigrated from Germany in the 1830s and 1840s, and Leeser founded a free Jewish school in his home, as well as traveled to address other synagogues.

He also allied with other religious minorities, notably Seventh Day Baptists, to advocate against Sunday blue laws that banned work and other activities on the "Christian Sabbath".

That paved the way for future Jewish seminaries in the United States, although it closed its doors in 1873 and Hebrew Union College would not be founded in Cincinnati until 1875.

[8] By the terms of his will, Leeser left his extensive collection of letters, pamphlets, books, and periodicals to Maimonides College, which closed in 1873.

The Leeser collection then passed to the Annenberg Research Institute, which became part of the University of Pennsylvania in 1993, as the Center for Advanced Judaic Studies.

[13] Leeser has been described as "a modern Orthodox Jew" because he hoped to create a "dynamic symbiosis of contemporary culture and Jewish tradition".

[14][15] He was also portrayed as "one [of] the most articulate spokesmen" among a small group of American Orthodox rabbis in the United States before the Civil War.

In addition, Leeser translated Joseph Schwarz's Geography of Palestine and, with Jaquett, published an edition of the Hebrew Bible.