Cambridge Center for Adult Education was founded as the Cambridge Social Union in 1870 whose mission was to provide a means of social and intellectual improvement.

In 1889 the Social Union purchased and moved into the William Brattle House at 42 Brattle Street, built in 1727. When living in the Brattle House, Loyalist General-Major William Brattle sparked the Powder House Alarm, an important prelude to the American Revolution. Brattle was later forced to evacuate Cambridge with other Loyalists and the home became the headquarters of George Washington’s aide-de-camp and quartermaster general, Thomas Mifflin. In the early years of the American Revolution, Brattle House hosted guests including Washington, John and Abigail Adams, and other well-known patriots.

Abraham Fuller purchased the Brattle House in 1831 and invited his brother’s family to move in. Margaret Fuller, an American journalist, critic, and women’s rights activist associated with the Transcendentalist movement, lived with her family at 42 Brattle Street until 1833. Fuller did not enjoy living in the mansion, describing it later as a “gilded cage.” It was during this time that Fuller had an epiphany while in church that she described as: "that there was no self; that selfishness was folly" and that she must teach herself to "act in cooperation with the constraints of life."

Cambridge Social Union became Cambridge Center for Adult Education (CCAE) in 1938. CCAE continues to honor Cambridge Social Union’s original mission of “providing a means of social and intellectual improvement.” Brattle House is listed on the National Register of Historic Places.

In 1972, CCAE acquired the Blacksmith House (the former Window Shop) property at 56 Brattle Street. Blacksmith House includes the Dexter Pratt House, built in 1808. Cambridge resident and poet Henry Wadsworth Longfellow observed Dexter Pratt, the blacksmith, at work under the spreading chestnut tree that stood in the yard. This sight inspired his poem “The Village Blacksmith.” In 1870 the tree was cut down when Brattle Street was expanded and the wood was used to make a chair for Longfellow.

In June 1870, the Blacksmith House came under the ownership of Mary Walker. Walker was born an enslaved woman in North Carolina. She escaped in 1848 to Philadelphia and settled in Massachusetts in 1850 to avoid the Fugitive Slave Law passed that year. Walker worked as a caretaker and seamstress, never ceasing her campaign to liberate her mother and children from enslavement. Walker was eventually reunited with three of her children at the end of the Civil War. A friend purchased Blacksmith House in Walker’s name and the home belonged to her, her children, and their descendants until the early 20th century.

After the Second World War, the Blacksmith House was home to The Window Shop, a Cambridge citizens’ organization that began in 1939 and assisted European refugees with training, counseling, and employment. It offered war refugees jobs in its clothing, crafts shop, tea room/bakery, known for its Viennese pastries, and restaurant, a popular gathering place for local European immigrants. The Window Shop was also one of the few, if not the first, Cambridge businesses to hire Black staff, including its chef.

To this day, the Center's historic buildings carry on its mission: providing social and intellectual opportunities for an increasingly diverse community.