Mill Basin is a residential neighborhood in southeastern Brooklyn, New York City. It is on a peninsula abutting Jamaica Bay and is bordered by Avenue U on the northwest and the Mill Basin/Mill Island Inlet on its remaining sides. Mill Basin is adjacent to the neighborhood of Bergen Beach to the northeast, Flatlands to the northwest, Marine Park to the southwest, and Floyd Bennett Field and the former Barren Island to the southeast. Mill Basin also contains a subsection called Old Mill Basin, north of Avenue U.

Mill Basin was originally Mill Island, Jamaica Bay. In the 17th century, a mill was built on Mill, Bergen, and Barren Islands. The archipelago was then occupied by the Schenck and Crooke families through the late 19th century, and remained a mostly rural area with oyster fishing. After Robert Crooke developed a smelting plant on Mill Island in 1890, industrial customers started developing the island and connected it to the rest of Brooklyn. In an effort to develop Mill Basin as a seaport district, ports and dry docks were built in the early 20th century, though a lack of railroad connections hindered the area's further growth. Residential development began in the late 1940s, along with the rest of southeast Brooklyn, though some of the former industrial buildings remain.

Mill Basin is primarily residential, with a mix of commercial and industrial uses, including the Kings Plaza shopping mall in its western part. The area around Mill Basin consists of a mostly white population as of the 2010 United States census, and is sparsely served by public transportation. Nearby recreational areas include Floyd Bennett Field, the first municipal airport in New York City, which is part of the Gateway National Recreation Area and is just southeast of Mill Basin.

Mill Basin is part of Brooklyn Community District 18, and its primary ZIP Code is 11234. It is patrolled by the 63rd Precinct of the New York City Police Department.

Originally, Mill Basin was an island in Jamaica Bay off the coast of Canarsie, called Mill Island. Most of the island was composed of low-lying meadows near sea level, but a very small part of it was arable uplands, or hilly areas above sea level. The area's original geography was vastly different from the modern geography.

A bulkhead was built along Mill Island's shore in the late 1890s. It was later connected to the uplands of nearby Bergen Beach, creating the continuous embankment between Mill and Paerdegat basins later used for the construction of the Belt Parkway. Most of the earliest filling operations along the island were private; the city government took over later. Some parts of Mill Basin remained a wetland until the late 20th century. A stream ran where Avenue U is today, dividing Mill Island from the mainland. Maps show that Mill Island was connected to the mainland by 1926, but modern city maps still allude to "Mill Island".

The New York Times described the neighborhood as a "mitten-shaped peninsula" enclosed to the south, west, and east by the eponymous waterway. Mill Basin is zoned as a predominantly residential neighborhood with one- or two-family residences. Small commercial overlays and recreational waterfront uses also exist, and the area between Avenue U and the Mill Basin waterway is zoned for heavy industry. Old Mill Basin is north of Avenue U. According to a map The New York Times published in 2009, Old Mill Basin can be considered to reach as far north as Avenue N.

The local Lenape Native Americans originally inhabited the area. They referred to the surrounding area, including Mill and Barren Islands, as "Equendito" or "Equindito", a name that probably means "Broken Lands". In 1624, the Dutch Republic incorporated much of the current New York City area into the colony of New Netherland. In 1636, as Dutch settlers expanded outward from present-day Manhattan, they founded the town of Achtervelt (later Amersfoort, then Flatlands) and purchased 15,000 acres (6,100 ha) around Jamaica Bay. Amersfoort was centered around the present-day intersection of Flatbush Avenue and Flatlands Avenue. Canarsie Indian leaders signed three land agreements with Dutch settlers between 1636 and 1667, ceding much of their historic land, including Mill Island. Mill Island, as well as the nearby Barren Island, was sold to John Tilton Jr. and Samuel Spicer in 1664. At some point in the 1660s or 1670s, a settler named Elbert Elbertse leased Mill Island, along with Bergen and Barren Islands.