a religious movement that has modified or abandoned many traditional Jewish beliefs, laws, and practices in an effort to adapt Judaism to the changed social, political, and cultural conditions of the modern world. Reform Judaism sets itself at variance with Orthodox Judaism by challenging the binding force of ritual, laws, and customs set down in the Bible and in certain books of rabbinic origin (e.g., the Talmud).

The movement began early in the 19th century, in Germany, with appeals from laymen for an updating of the Jewish liturgy and other rituals. With the liberation of Jews from their ghettos, many Jews began to question their allegiance to such traditions as restrictive dietary laws, prayers in Hebrew, and the wearing of special outfits that set them apart as Jews. Many felt that Judaism would lose Jews to other religions if steps were not taken to bring Judaism into the 19th century.

Israel Jacobson (1768–1828), a Jewish layman, established an innovative school in Seesen, Brunswick, in 1801. There he held the first Reform services in 1810, attended by adults as well as children. Jacobson's liturgy was in German rather than Hebrew; organ and choir music were added to the service; and Jacobson instituted confirmation for both boys and girls to replace the traditional boys' bar mitzvah ceremony. The liturgy omitted all references to a personal messiah who would restore Israel as a nation. Jacobson held Reform services in Berlin in 1815; and from there Reform practices spread to Denmark, Hamburg, Leipzig, Vienna, and Prague.

Although the Prussian government issued prohibitions under pressure from Orthodox leaders, the movement could not be stifled. Reform worshippers were no longer required to cover their heads or wear the prayer shawl (ṭallit). Daily public worship was abandoned; work was permitted on the Sabbath; and dietary laws (kashrut) were declared obsolete.

Rabbi Abraham Geiger (Geiger, Abraham) (1810–74) was one of the leading ideologists of the Reform movement. He concluded that the essence of Judaism is belief in the one true God of all mankind, the practice of eternally valid ethical principles, and the communication of these truths to all nations of the world. Samuel Holdheim (Holdheim, Samuel) (1806–60) rejected Jewish marriage and divorce laws as obsolete, arguing that such codes fell outside the ethical and doctrinal functions of Judaism and were superseded by the laws of the state. He agreed with Geiger that monotheism and ethics are the principal criteria of authentic Judaism. Both felt that Judaism must be a living, constantly developing faith, compatible with the spirit of the times.

Rabbi Isaac Mayer Wise (Wise, Isaac Mayer) (1819–1900), a German emigrant, was a central figure in the remarkable success of Reform Judaism in the United States, where it had begun in 1841 when a congregation in Charleston, S.C., joined the Reform movement. Wise not only issued a widely influential prayer book (1857) but eventually established the Union of American Hebrew Congregations (1873), the Hebrew Union College (1875) for the education of Reform rabbis, and the Central Conference of American Rabbis (1889).

Two other emigrants, David Einhorn (1809–79) and Samuel Hirsch (Hirsch, Samuel) (1815–89), provided the theoretical foundations of American Reform. Hirsch was chairman of the first conference of American Reform rabbis, which met in Philadelphia in 1869. It declared that Jews should no longer look forward to a return to Palestine, and it rejected belief in bodily resurrection after death. The question of Zionism, support for an independent Jewish nation, was controversial within the Reform movement until the establishment of Israel in 1948.

In 1937 several fundamental principles of earlier Reform Judaism were dramatically revised. In that year an important conference of Reform rabbis issued the Columbus (Ohio) Platform, supporting the use of traditional customs and ceremonies and the liturgical use of Hebrew. In the late 20th century the Central Conference of American Rabbis continued to debate how best to continue the spirit of the Reform movement. It issued several new prayer books for the modern age and considered such issues as inclusion of single parents in the congregation, the position of women in the congregation and in the rabbinate, and homosexuality.