Harriet was a Galápagos tortoise who had an estimated age of 175 years at the time of her death in Australia. Harriet is one of the longest-lived known tortoises, behind Tu'i Malila, who died in 1966 at the age of 188 or 189; Jonathan, who remains alive at an age of 191, and possibly Adwaita, who died in 2006 at an estimated age of between 250 and 255 years. At the time of her death, she lived at the Australia Zoo which was owned by Steve and Terri Irwin.

The Galápagos tortoise or Galápagos giant tortoise is a very large species of tortoise in the genus Chelonoidis. The species comprises 15 subspecies. It is the largest living species of tortoise, and can weigh up to 417 kg (919 lb). They are also the largest extant terrestrial cold-blooded animals (ectotherms).