Brunswick School is an all-boys college-preparatory private day school located in Greenwich, Connecticut, United States. It includes pre-kindergarten, a Lower School (grades 1–4), a Middle School (grades 5–8), and a high school, or, as it is called within the Brunswick Community, Upper School (grades 9–12).
The school's mascot is the Bruin, and its colors are brown, white, and gold.
The present Headmaster and Head of the Upper School is Thomas Philip. The present Lower and Middle School Heads are Kathleen Signer and Sarah Burdett, respectively.
The school motto is "Courage, Honor, Truth." The school proverb is "With All Thy Getting, Get Understanding."
Brunswick School was founded in 1902 by George B. Carmichael, a teacher at the nearby Greenwich Academy. The school is a college preparatory day school serving approximately 930 boys in grades pre-kindergarten through 12. 
Brunswick school is made up of two main campuses. The Upper School campus is located on Maher Avenue in Greenwich. The Upper School english and history annex is located on North Maple Avenue, a short walk from the main Upper School facility. The Edwards Campus (named after former headmaster Duncan Edwards, II) is located about 15 minutes away from the Maher Avenue campus on King Street. The Edwards Campus is made up of the Pre School, Lower School, and Middle School facilities, along with the Burke Fieldhouse (basketball, wrestling, tennis, and the Cosby Weight Room) and Sampson Fieldhouse (which houses the Dann O'Neil Gym, the Stephens Squash Courts, and Hartong Rink). A facility dedicated to science and arts for Upper School students located on the Edwards Campus shares a building with the Pre School. Additionally, Brunswick owns a boat house located on River Road, just a twenty-minute drive from the Upper School campus. Brunswick recently purchased a property in Vermont which will house specially designed programs for underclassmen boys to attend for a few days out of the school year. 
Brunswick's sister school is Greenwich Academy, which is located two blocks from Brunswick's Upper School campus. The two schools share classes with each other during Upper School, and students are able to choose courses from a combined course catalogue, with the exception of mathematics courses and ninth grade English, which remain separate.  The connection between "" Greenwich Academy"" and Brunswick dates back to the school's founding. The founder of Brunswick had been previously employed as a teacher at Greenwich Academy, which was then a co-educational secondary school. After the founding of Brunswick, Greenwich Academy began admitting girls alone, directing boys to apply to Brunswick School. 
- Akin Akingbala, former basketball player for Clemson University and the Boston Celtics
- Hayward Alker, international relations scholar
- Neil Burger, film director
- Peter Corroon, former mayor of Salt Lake County, Utah
- Peter Fonda, actor
- Pete Francis Heimbold, former member of the band Dispatch
- Matthew Heineman, Oscar-nominated filmmaker
- Justin Henry, actor
- Chris Jenkins (sound engineer), Oscar-winning sound engineer
- Hugh Jessiman, hockey player
- Rod Lurie, Film director
- Mitch Marrow, American football player
- Justin McAuliffe, businessman and member of the Hilton family
- Kevin Shattenkirk, hockey player
- Alex Shibutani, Olympic figure skater
- Bill Simmons, sports columnist
- Christopher Tsai, investment manager and art collector
- Cameron Winklevoss, Olympic rower and social networking pioneer
- Tyler Winklevoss, Olympic rower and social networking pioneer
- Brad Seaton, Football player at Villanova, NFL Offensive Tackle
- Mehra Natatorium
- Burke Field House
- Sampson Athletic Center
- Atta, John R. Van (2001). A place for boys : Brunswick School and the building of young men. Greenwich, Conn.: The School. ISBN 097116150X.
- "Archived copy". Archived from the original on 2009-02-21. Retrieved 2009-02-27.
- Brunswick School (2014). "Course Catalogue 2014-2015". Brunswick School. pp. 8, 28. Archived from the original on 2014-05-23. Retrieved 2014-05-23.
- Greenwich Academy. "Greenwich Academy: History". Greenwich Academy. Archived from the original on 2014-05-24. Retrieved 2014-05-23.