Sidwell Friends School is a private, college preparatory, Quaker school located in Bethesda, Maryland, and Washington, D.C., offering pre-kindergarten through high school classes. Founded in 1883 by Thomas W. Sidwell, its motto is "Eluceat omnibus lux" (English: Let the light shine out from all), alluding to the Quaker concept of inner light.

The school is private with a merit-based admissions process. As documented on the school's website, it gives preference in admissions decisions to members of the Religious Society of Friends but otherwise does not discriminate on the basis of religion. Sidwell "accepts only 7 percent of its applicants." The school accepts vouchers under the D.C. Opportunity Scholarship Program.

The school has educated children of notable politicians, including those of several presidents. President Theodore Roosevelt's son Archibald, President Richard Nixon's daughters Tricia and Julie, President Bill Clinton's daughter Chelsea Clinton, President Barack Obama's daughters Sasha and Malia, President Joe Biden's grandchildren when he was Vice President and Vice President Al Gore's son, Albert Gore III, graduated from Sidwell Friends.

Thomas Sidwell started a "Friends' Select School" in 1883 on I Street in downtown Washington, four blocks from the White House. It opened with just eleven students.

In 1911, Sidwell began buying property between Wisconsin Avenue and 37th St. Initially, the new property was used for athletic fields—and, with the central campus's downtown location—meant students had to shuttle between the two sites by streetcar. However, in 1923, Sidwell built a building for school dances and other social gatherings on what came to be known as the Wisconsin Avenue campus.

In 1925, the school added a kindergarten, making it the first K–12 school in Washington, D.C. In 1934, the name of the school was changed to "Sidwell and Friends School." In 1938 it acquired the former Washington, D.C. estate of Rear admiral Cary T. Grayson, Highlands, and began its gradual re-location to its Wisconsin Avenue building. By 1938, the transition to the new building had been completed, and the I Street property was sold.^{[citation needed]}

In 1957, the school adopted a formal dress code policy, with requirements and recommendations for boys and girls in Kindergarten, Lower School, Middle School, and Upper School. The dress code continued to evolve to include further restrictions on hair length, skirt length, and types of shoes in the 1960s, but began to relax by 1969. Following student proposals and negotiations, the dress code was modified in the early 1970s and by 1975 permitted jeans to be worn by students. The dress code continued to evolve in the 1980s and by 2000 included restrictions on exposed midriffs and visible underwear. In 2016, students led a change to the dress code to ban clothing with the Washington Redskins (currently the Commanders) football team name and logo.

Previously, all grade levels were in Washington, D.C. In 1963, the elementary school moved to the former Longfellow School for Boys, purchased by Sidwell Friends.