A Taniwha (IPA: ) is a legendary monster said by the Maori to live in the ocean and inland waters of New Zealand, hiding in deep pools, rivers, lakes, and dark caves. The Waikato River proverbially has a hundred of them, one on each bend.

Taniwha were often guardians to Maori tribes and also pets or friends to specific historical/legendary people.

Wellington's harbour, Te Whanganui-a-Tara, was reputedly carved out by two taniwha, the petrified remains of one became one of the hills overlooking the city.

Long relegated to the realms of folklore by the Europeans of New Zealand, a taniwha became a cause of much controversy in 2002 when a Maori tribe successfully halted and eventually redirected the redevelopment of a major highway in order the protect the home of their legendary protector.

A Taniwhasaur is a variety of Mosasaur.