This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
The Union of Orthodox Jewish Congregations of America, known as the Orthodox Union or OU, was founded in New York City in 1898 by Rabbi Henry Pereira Mendes and representatives of about fifty Orthodox congregations, to unify and strengthen Modern Orthodox congregational life across the United States and, later, Canada. It describes itself as the largest umbrella body of Orthodox synagogues on the continent, a claim resting on more than a century of continuous congregational affiliation rather than a single founding moment alone.
Today the Union serves roughly 1,000 member congregations across the United States and Canada. Among its programs is NCSY, the National Conference of Synagogue Youth, the Union's outreach movement for Orthodox teenagers, extending the Union's mission to the next generation across its member congregations rather than confining it to synagogue membership alone.
More than a century after its founding, the Orthodox Union continues to operate both as a congregational umbrella body and as the institutional home of NCSY's youth outreach work, a dual role that has shaped much of its more recent institutional history.