Anacostia /ænəˈkɒstiə/ is a historic neighborhood in Southeast Washington, D.C. in the United States. Its downtown is located at the intersection of Marion Barry Avenue (formerly Good Hope Road) SE and Martin Luther King Jr Avenue SE. Originally known as "Uniontown" the neighborhood contains commercial and government buildings, mid-rise mixed development, city-sanctioned art murals and galleries (under the "Art to Go Go" initiative), a performing arts center, a playhouse theater, the local landmark, "The Big Chair," Frederick Douglass's Home (a museum and historic site) and is adjacent to the Fort Stanton Park neighborhood which hosts the Smithsonian affiliated Anacostia Community Museum. Anacostia is located directly east of and along the Anacostia River, after which the neighborhood is named. The community's population is more than 90 percent African American.

Bounded by the Southeast Freeway to the north and northwest, the Suitland Parkway to the south and southwest as well as Fort Stanton and Ricketts Park to the east, Anacostia includes all of the Anacostia Historic District, which was listed on the National Register of Historic Places in 1978. The Frederick Douglass National Historic Site preserves the famous 19th century civil rights leader's home. The Anacostia Community Museum is part of the Smithsonian. Often the name "Anacostia" is used to refer to the entire portion of the city that is southeast of the Anacostia River. The Anacostia Business Improvement District is responsible for the development of the area.

The name "Anacostia" comes from the anglicized name of a Nacochtank settlement along the Anacostia River. Archaeological evidence indicates that American Indians settled in the Washington, D.C., area at least 4,000 years ago, close to the Anacostia River. Native inhabitants within the present-day District of Columbia included the Nacotchtank, at Anacostia, who were affiliated with the Conoy.

Captain John Smith explored the area in 1608, traveling up the "Eastern Branch"—later the Anacostia River—mistaking it for the main body of the Potomac River, and met Anacostans. Before the arrival of whites, the Nacostine villages in this area were a lively center of trade visited by Native Americans such as the Iroquois of New York. Even after the founding of Maryland, Leonard Calvert, in a letter to a merchant in London, described "Anacostan" as one of the three best places in the colony for trading with natives.

Around the year 1668, native peoples previously living south of Anacostia were forced northward by war. Anacostine Island, which first appeared on a 1670 map drawn by Augustine Herman, was settled by the Anacostans around this time.

The core of what is now the Anacostia historic district was incorporated in 1854 as Uniontown and was one of the early suburbs in the District of Columbia. It was designed to be affordable for Washington's working class, many of whom were employed across the river at the Navy Yard; its (then) location outside of and isolated from the city made its real estate inexpensive. The initial subdivision of 1854 carried restrictive covenants prohibiting the sale, rental or lease of property to anyone of African or Irish descent.

During the Civil War, Anacostia was protected by a series of forts upon the hills southwest of the city. Following the conclusion of the war, the forts were dismantled and the land returned to its original owners.

Abolitionist Frederick Douglass, often called "the sage of Anacostia", bought Cedar Hill, the estate belonging to the developer of Uniontown, in 1877 and lived there until he died in 1895. The home is still maintained as the Frederick Douglass National Historic Site in Anacostia.