The Mattaponi (English: /ˌmætəpoʊˈnaɪ/) tribe is one of only two Virginia Indian tribes in the Commonwealth of Virginia that owns reservation land, which it has held since the colonial era. The larger Mattaponi Indian Tribe lives in King William County on the reservation, which stretches along the borders of the Mattaponi River, near West Point, Virginia.

The Mattaponi were one of six tribes inherited by the leader of the Confederacy, Mamanatowick Powhatan, in the late 16th century. The tribe spoke an Algonquian language, like other members of the Powhatan Confederacy. The confederacy numbered more than 30 members by the time the English arrived and settled Jamestown in 1607.

In addition, a Mattaponi band had long been settled outside the reservation at an unincorporated hamlet called Adamstown, located on the upper reaches of the Mattaponi River. This has been identified as Indian land in records dating to the 17th century. In 1921, this Upper Mattaponi Tribe of Adamstown organized as an official group. They have been recognized as a tribe by the Commonwealth of Virginia and own 32 acres (130,000 m²) of land in King William County. Federal status was granted to the Upper Mattaponi Tribe through the passage of the Thomasina E. Jordan Indian Tribes of Virginia Federal Recognition Act of 2017 on January 12, 2018.

The Mattaponi Indians legally became a branch of Pamunkey Indians, who are also federally recognized. The Mattaponi and Pamunkey have a similar cultural foundation, and were members of the same Confederacy.

According to archaeologists, indigenous peoples of successive cultures have been living in the area now called Virginia for as long as 15,000 years. The Mattaponi are believed to have formed in the 14th and 15th centuries. They were surrounded by nations speaking various languages including : Algonquian along the coast and in the Tidewater, Siouan in the central area and Piedmont, and Iroquoian generally in the backcountry and to the north.

In 1607, the Mattaponi were identified by name by the English explorers John Smith, who noted that they were living along the Mattaponi River. William Strachey estimated their warriors at 140, meaning their population likely numbered about 450.

During the second Anglo-Powhatan War of 1644–1646, the Mattaponi fled their homeland along the Mattaponi River and took refuge in the highlands along Piscataway Creek. With the cessation of hostilities, they gradually returned to its homeland. In 1646, at the conclusion of the Anglo-Powhatan War, the Powhatan Confederacy signed their first treaty with the English. By treaty, the English defined the tribes as tributaries; they allocated reservations lands for several of the tribes, in exchange for requiring an annual tribute payment of fish and game.

In 1656–1657, the leaders of the Mattaponi Tribe signed peace treaties with the Court of Rappahannock County and the justices of Old Rappahannock County. Tribal members were to be treated equally as Englishmen in court and civil rights.