Isabella Stewart Gardner (April 14, 1840 – July 17, 1924) was an influential American art collector, philanthropist, and patron of the arts whose collection is now housed in the Isabella Stewart Gardner Museum, in Boston, Massachusetts.

Isabella Stewart, daughter of David and Adelia (Smith) Stewart, was born in New York City, New York. She married John Lowell "Jack" Gardner, son of John L. and Catharine E. (Peabody) Gardner of Boston, Massachusetts on April 10, 1860 in New York City and thereafter moved to Boston. Jack Gardner's grandfather was the distinguished Salem shipowner, Joseph Peabody, who made a fortune importing pepper from Sumatra and was one of the wealthiest men in the United States at the time of his death in 1844.

During her lifetime, the Boston society pages called her many names, including "Belle," "Donna Isabella," "Isabella of Boston," and "Mrs. Jack." Gardner created much fodder for the gossip tabloids of the day with her reputation for stylish tastes and unconventional eccentricities. After she and her husband missed the train to a social engagement, she persuaded the railroad to lend them another for their own personal use. Her surprising appearance at a 1912 concert (at what was then a very formal Boston Symphony) wearing a white headband emblazoned with "Oh, you Red Sox" was reported at the time to have "almost caused a panic", and remains still in Boston one of the most talked about of her eccentricities.

After her husband's death in 1898, Gardner began work on her museum. Completed in 1903, the museum was named "Fenway Court" and constructed in the reclaimed swamplands of Boston's Fenway area. Modeled on the Renaissance palaces of Venice, Italy, it was designed by Willard T. Sears, with much direct involvement from Gardner, to accommodate the art and architectural artifacts Gardner had collected with her husband over many years. The building completely surrounds a glass-covered garden courtyard. The first through third floors were designed to be galleries. The fourth floor of the building was used as living quarters by Gardner until her death in 1924, and is now used for offices. Gardner insisted that the galleries be designed as a palatial home, not a museum, and in the early years after the building was completed she used those floors as such, opening them to the public just 20 days a year.

She died at Fenway Court at age 84, and was buried in the Gardner family tomb at Mount Auburn Cemetery in Cambridge, Massachusetts. She was a friend of noted artists and writers of the day, including John Singer Sargent, James McNeill Whistler, Anders Zorn, Henry James, Okakura Kakuzo and Frank Marion Crawford.

Shortly after midnight on the morning of March 18, 1990, thieves disguised as police officers talked their way into the museum. They handcuffed the two on-duty security guards out of sight and then stole thirteen works of art valued at over $500 million, including The Concert, one of Johannes Vermeer's thirty-four known paintings, and three works by Rembrandt van Rijn, including his only seascape, The Storm on the Sea of Galilee, and a small self-portrait print. Also stolen were a series of drawings by Edgar Degas and additional works by Édouard Manet and Govaert Flinck, as well as two objects: a Chinese Ku, or beaker, and a finial from a Napoleonic flag. It is considered the biggest art theft—and property theft—in history; the crime remains unsolved. The museum still displays the paintings' empty frames in their original locations according to the strict provisions of Gardner's will, which instructed that the collection be maintained unchanged.

In September 2004 and February 2005, there were reports in Variety, the Boston Herald and The Boston Globe about a new theory emerging on the theft. In early February 2005 the FBI flew an American art dealer from New York to Paris to meet with the French National Police and pursue new leads that have, thus far, not resulted in any significant advance in the case. [6]

In late 2005, as part of a concerted effort to enhance security, the museum hired a former Homeland Security official who helped to rebuild security at Logan Airport after the events of September 11, 2001. MAC Systems and General Electric also conducted a large-scale and comprehensive upgrade to the facility's access control system. More upgrades are in the works to ensure that the events of March 18, 1990 are never repeated.

The thefts are a subject of a 2005 documentary called Stolen, which in a slightly different version had earlier appeared on Court TV. In 2009, HarperCollins plans to release a book on the theft called The Gardner Heist, written by journalist Ulrich Boser. The book boasts of being able to reveal the identities of the thieves.