botanical gardens in Kennett Square, near Philadelphia, Pennsylvania, U.S. The gardens are operated by Longwood Gardens, Inc., a private foundation, which, in cooperation with the U.S. Department of Agriculture and other public horticultural institutions, sponsors expeditions to many parts of the world in search of ornamental plants for introduction into the United States.

The land now occupied by the gardens was acquired from William Penn (Penn, William) in about 1700 by the Peirce family, who named it Long Woods. Two members of the family, Joshua and Samuel Peirce, began planting exotic trees there in 1798. The property, subsequently known as Peirce's Park, was acquired in 1906 by industrialist Pierre Samuel du Pont (du Pont, Pierre Samuel), who renamed it Longwood, developed its conservatories (1919–21), and created the foundation (1937). The foundation took over operation of the gardens in 1946.

The gardens now occupy 1,050 acres (425 hectares) and contain extensive collections of native, tropical, and subtropical plants, totaling some 11,000 different varieties. In addition to the horticultural exhibits, the gardens include a museum in the old estate house and an open-air theatre.