The 'I'iwi (Vestiaria coccinea) or Scarlet Hawaiian Honeycreeper is a Hawaiian bird of the family Drepanididae, and the only member of the genus Vestiaria. One of the most plentiful species of this family, which includes many endangered or extinct species, the 'I'iwi is a highly recognizable symbol of Hawai'i.

The adult 'I'iwi is mostly fiery red, with black wings and tail and a long curved salmon-colored bill used primarily for drinking nectar. Though rare, the contrast of the red and black plumage with surrounding green foliage makes the 'I'iwi one of the most easily seen Hawaiian birds. Younger birds have more spotted golden plumage and ivory bills and were mistaken for a different species by early naturalists in Hawai'i.

The 'I'iwi's feathers were highly prized by Hawaiian ali'i (nobles) for use in decorating 'ahu'ula (capes) and mahiole (helmets), and such uses gave the species its scientific name: vestiaria comes from the Latin for clothing, and coccinea means scarlet-colored. The bird is also often mentioned in Hawaiian folklore.

Although the long bill of the 'I'iwi apparently evolved for feeding from long curved flowers, the bird now depends primarily on nectar from 'ohi'a trees, which have tiny flowers. 'I'iwi bill size has apparently shrunk in the past 100 years due to this change in food supply, according to researchers at the University of Hawai'i. In addition to 'ohi'a blossoms, the 'I'iwi also feeds on nectar from lobelia flowers, and on insects and larvae.

'I'iwi breed mostly from February to September. Clutches of one to three whitish eggs with dark brown markings are laid in cup-shaped nests made up of leaves, lichens, and moss. The eggs hatch after about fourteen days. The newly hatched chicks have bright orange skin, with patches of soft down feathers on their small head and wings. After approximately after three weeks, the fledglings grow speckled yellow-green feathers. The red adult plumage gradually appears first on the breast, then spreads to the head.

Although 'I'iwi are still fairly common on most of the Hawaiian islands, it is rare on O'ahu and Moloka'i and no longer found on Lana'i. Most of the decline is blamed on loss of habitat, as native forests are cleared for farming, grazing, and development.

Another threat has been the spread of introduced diseases, particularly avian malaria (Plasmodium relictum), which is spread by mosquitoes. In a series of challenge experiments involving avian malaria, more than half of the 'I'iwi tested died from a single infected mosquito-bite. Thus the 'I'iwi generally survives at higher elevations where temperatures are too cool for mosquitoes, and like many disease-susceptible endemic birds is rare to absent at lower elevations, even in relatively intact native forest.

On Moloka'i, The Nature Conservancy has attempted to preserve habitat by fencing off areas within several nature reserves to keep out pig populations. The pigs create wallows which serve as incubator sites for mosquito larvae, which in turn spread avian malaria.