The tribe is named after the Waikato River, which plays a large part in its history and culture.

[2][3] Pōtatau Te Wherowhero, the first Māori king, was a member of the Ngāti Mahuta hapu (sub-tribe) of Waikato iwi, and his descendants have succeeded him.

The marae are spread over a large area from Te Kūiti and Cambridge in the south to Auckland in the north.

The Waikato-Tainui tribal administration (or iwi authority) is the Waikato Raupatu Trustee Company Ltd, which replaced the Tainui Māori Trust Board, and is situated at Hopuhopu, Ngāruawāhia.

[2][3] There have traditionally been strong links between Tainui and the University of Waikato, which has strengths in Māori language and modern local history.