Washington University in St. Louis (WashU, or WUSTL) is a private research university in Greater St. Louis with its main campus (Danforth) mostly in unincorporated St. Louis County, Missouri, and Clayton, Missouri. It also has a West Campus in Clayton, North Campus in the West End neighborhood of St. Louis, Missouri, and Medical Campus in the Central West End neighborhood of St. Louis, Missouri.

Founded in 1853 and named after George Washington, the university has students and faculty from all 50 U.S. states and more than 120 countries. Washington University is composed of seven graduate and undergraduate schools that encompass a broad range of academic fields. To prevent confusion over its location, the Board of Trustees added the phrase "in St. Louis" in 1976. Washington University is a member of the Association of American Universities and is classified among "R1: Doctoral Universities – Very high research activity".

As of 2020, 25 Nobel laureates in economics, physiology and medicine, chemistry, and physics have been affiliated with Washington University, ten having done the major part of their pioneering research at the university. In 2019, Clarivate Analytics ranked Washington University 7th in the world for most cited researchers. The university also received the 4th highest amount of NIH medical research grants among medical schools in 2019