Tainui may refer to:
- Tainui, a confederation of Māori iwi (tribes) in New Zealand
- Waikato Tainui, often referred to as "Tainui", a constituent tribe of the abovementioned confederation
- Tainui (canoe), a Māori waka (migration canoe)
- Tainui, New Zealand, a suburb of Dunedin
- Tainui (New Zealand electorate), a former parliamentary Māori electorate.
- SS Tainui, a Royal Navy cargo ship that was torpedoed in 1918