Anna's hummingbird (Calypte anna) is a North American species of hummingbird named after Anna Masséna, Duchess of Rivoli.

It is native to western coastal regions of North America. Until the late 20th century, Anna's hummingbirds migrated from locations as far north as Alaska and coastal British Columbia, returning south to breed in Baja California and Southern California.

Since the 1970s, ornamental plants in residential areas along the Pacific coast and inland deserts provided expanded nectar and nesting sites, allowing the species to expand its breeding range to northern coastal regions without migrating. Year-round residence of Anna's hummingbirds in the Pacific Northwest is an example of ecological release dependent on acclimation to colder winter temperatures, introduced plants, and human provision of nectar feeders during winter.

These birds feed on nectar from flowers using a long extendable tongue. They also consume small insects and other arthropods caught in flight or gleaned from vegetation.

Anna's hummingbird was formally described and illustrated in 1829 by the French naturalist René Lesson in his Histoire naturelle des Oiseaux-Mouches from a specimen that had been collected in California. Lesson placed it in the genus Ornismya and coined the binomial name Ornismya anna. Anna's hummingbird is now placed in the genus Calypte that was introduced in 1856 by the English ornithologist John Gould. Gould did not explain the derivation of the genus name but it is probably from the Ancient Greek kaluptrē meaning "woman's veil" or "head-dress" (from kaluptō meaning "to cover"). The specific epithet anna was chosen to honour Anne d'Essling who married the ornithologist François Victor Massena, 3rd Duke of Rivoli. The species is monotypic: no subspecies are recognised.

Anna's hummingbirds are 3.9 to 4.3 in (9.9 to 10.9 cm) long with a wingspan of 4.7 inches (12 cm) and a weight range of 0.1 to 0.2 oz (2.8 to 5.7 g). They have an iridescent bronze-green back, a pale grey chest and belly, and green flanks. Their bills are long, straight, and slender. The adult male has an iridescent crimson-red, derived from magenta, to a reddish-pink crown and gorget, which can look dull brown or gray without direct sunlight, and a dark, slightly forked tail. Females also have iridescent red gorgets, although they are usually smaller and less brilliant than the male.

The male Anna's hummingbird is the only North American hummingbird species with a red crown. Females and juvenile males have a dull green crown, a grey throat with or without some red iridescence, a grey chest and belly, and a dark, rounded tail with white tips on the outer feathers.

The male has a striking reddish-pink crown and gorget, which are strongly iridescent and dependent on the angle of illumination and observation by female or male competitor birds. The iridescence results from large stacks of melanosomes in the feather barbules, occurring as layers separated by keratin. The barbules reflect incident light in the manner of partially-opened Venetian blinds, enabling the iridescence – which varies the head and gorget coloration with the changing angle of light – as a coloration advantage for courtship attraction and territory defense.