OU.org (Orthodox Union)
The Orthodox Union's home — the standard kashrut certification, plus comprehensive Orthodox educational and pastoral resources.
Summary. OU.org is the website of the Orthodox Union, the umbrella organization of Modern Orthodox congregations in North America. It is the standard kashrut authority (the OU symbol on packaged food). The website offers extensive holiday guides, halachic Q&A, Torah classes (the OU's Torah Tidbits weekly publication, OU Press books, the All Daf Talmud app), and pastoral resources. The OU is the standard reference for Modern Orthodox practice.
Kashrut
The OU symbol (a U inside an O) on a packaged food product certifies that food as kosher under OU supervision. The OU is the largest of the kashrut agencies and is universally accepted across the Orthodox spectrum (with the exception of some Haredi communities that prefer their own certifications). The OU Kosher website (oukosher.org) maintains a searchable database of certified products and an active Q&A service for questions about specific products.
Halacha Yomit and Educational Programs
The OU runs Halacha Yomit, a daily halacha email; the Torah Tidbits weekly parshah publication; the All Daf Talmud companion app for Daf Yomi learners; and a substantial library of online classes. The OU's NCSY youth movement runs summer programs, gap year programs in Israel, and the regional shabbatonim that have introduced thousands of teenagers to observant Judaism.
Tzedakah and Advocacy
The OU's Advocacy Center represents Orthodox interests in Washington. The OU's Yachad program serves Jews with disabilities; the Department of Community Engagement supports young rabbis and synagogues.
Where Denominations Diverge
Modern Orthodox. The OU's positions are normative for North American Modern Orthodoxy.
Sources
OU.org and OUKosher.org
Further Reading
TorahTidbits.com — the OU's weekly parshah publication.
All Daf Talmud companion app.