American religious organization dedicated to preserving and promoting Jewish (Jew) social and religious values in the United States and to strengthening ties between U.S. and Israeli (Israel) Jewish communities.

The organization is one of the largest volunteer women's organizations in the United States; in the early 21st century it had more than 300,000 members. It was founded in 1912 by Jewish scholar and activist Henrietta Szold (Szold, Henrietta) and other women as the Hadassah Chapter of the Daughters of Zion. In 1914 the organization changed its name to Hadassah, the Hebrew name for the biblical Queen Esther.

Within its first year the organization opened a medical institution in Palestine, marking the beginning of its commitment to the provision of medical services. In 1918 it established the Henrietta Szold Hadassah School of Nursing to provide staff for the facility. Since then Hadassah has financed, established, and maintained a large number of health-care-related services and facilities in Israel, which serve those in need regardless of their religious affiliations. It also is involved in environmental projects, including tree planting and the creation of parks.

In the United States Hadassah's national educational department publishes study guides on Jewish history and culture and produces a number of periodicals. Local chapters of the organization also sponsor Zionist youth programs and provide resources to American Jews wishing to migrate to Israel.