The Baldwin School (simply referred to as Baldwin School or Baldwin) is a private school for girls in Bryn Mawr, Pennsylvania, United States. It was founded in 1888 by Florence Baldwin.

The school occupies a former nineteenth-century resort hotel that was designed by Victorian architect Frank Furness, a landmark of the Philadelphia Main Line. The building was added to the National Register of Historic Places in 1979.

Baldwin's brother school is the Haverford School, in nearby Haverford. The Baldwin School is not religiously associated.

In 1888, Florence Baldwin founded "Miss Baldwin's School for Girls, Preparatory for Bryn Mawr College" in her mother's house at the corner of Montgomery and Morris Avenues in Bryn Mawr, Pennsylvania. The first class was composed of thirteen girls.

The second Bryn Mawr Hotel was designed by Furness, Evans & Company and was built between 1890 and 1891. It is a five-story, L-shaped, stone-and-brick building that was created in a Renaissance Revival / châteauesque style, and features a large semi-circular section at the main entrance, topped by a conical roof and finial. It has a steeply pitched red roof with a variety of dormers, chimneys, towers, finials, and skylights.

In 1896, The Baldwin School began leasing the Bryn Mawr Hotel during the winter months for use as a dormitory for its boarding students. They leased it year-round beginning in 1912. In 1922, the school purchased the building and the surrounding 25 acres (100,000 m) for $240,000.

Today the school has made many additions to "The Residence," but maintained the general style of the original building. It is now used for dining, art studios, theater performances, housing, the Middle School, and an Early Childhood Center.

A two-story science building opened in 1961; it was enlarged in 1995 to accommodate the increasing number of students. The Upper School inhabits the three-story Schoolhouse, which was built in 1926. It was renovated in 1997.

Renovations completed in 2014 to "The Residence" specifically support the Pre-Kindergarten and Kindergarten classes. In 2015, a performing arts center was built called The Simpson Center, which can be used for many different events.

The school formally opened a new athletic center in 2008. It has a six-lane swimming pool, gymnasium, three-lane jogging track, four squash courts, a fitness center, five tennis courts, and a practice field.

Students of color represent 40% of the student body.

Baldwin's music education begins in the Lower School. Students receive twice weekly music classes and sing in weekly choruses in Grades 3–5. Students perform in musical plays once a year. In Middle School, chorus, orchestra and classes in guitar and hand bell are available. In Upper School, ensembles include a jazz band, a classical chamber music ensemble, two hand bell choirs, vocal ensembles, and an orchestra.

The Middle School Chorus participates annually in the Music in the Parks competition at Hershey Park in May. At the 2014 competition, the Middle School Chorus received a Superior rating and the Best Overall Middle School Chorus trophy for their performances. The B-Flats are the acapella group for Upper Schoolers at Baldwin, and travels to Denmark every three years. The B-flats have won the Ardmore Rotary in 2022, 2023, and 2024

The Baldwin School competes in the Inter-Academic League, most commonly known as the Inter-Ac. Interscholastic varsity sports are: Basketball, Cross-Country, Field Hockey, Golf, Lacrosse, Rowing, Soccer, Softball, Squash, Swimming and Diving, Tennis, Volleyball, and Indoor Track. Dance is also offered, and students also have the option of Independent PE if they are seriously committed to a sport outside of school such as horseback riding or ice skating, or any sport included in Baldwins program. Athletes who do participate in IPE are required to play their sport for Baldwin during the season if it is an offered sport. PE is another option, which is during the school day, for either 45 or 70 minutes.

Baldwin has tennis, softball, squash, and lacrosse teams. The Baldwin Bears have recently been Inter-Ac champions in softball, lacrosse, and squash. Its longtime local rival has been the Episcopal Academy in Newtown.

Baldwin is best known for its squash program. Each class regularly consists of a couple nationally ranked squash players, many of whom compete internationally across Europe, Canada, and South America. Several Baldwin Squash alumni have gone to play the sport at various Ivy League schools. Many of these players are also among the strongest academically at Baldwin, earning honors including National Merit and induction into the Cum Laude Society.

Baldwin's longstanding rival in squash has been Greenwich Academy in Connecticut. In 2015, the upper school team defeated Greenwich in the US Squash Championships at Trinity College. The school's middle school team won the national championship against Greenwich in 2016 and 2018. The upper school team again faced Greenwich in the 2018 national championships, but lost 1–6. However, in 2019, Baldwin was able to defeat Greenwich 5–2 in the national championships. This ended a 3-year streak of Greenwich being the reigning national champions.

• Official website
• Main Line Today magazine
• Petersen's Private Secondary Schools
• National Coalition of Girls' Schools
• National Association of Independent Schools
• History of the Main Line