The white-breasted nuthatch (Sitta carolinensis) is a species of bird in the nuthatch family Sittidae. It is a medium-sized nuthatch, measuring approximately 15.5 cm (6.1 in) in length. Coloration varies somewhat along the species' range, but the upperparts are light blue-gray, with a black crown and nape in males, while females have a dark gray crown. The underparts are whitish, with a reddish tinge on the lower abdomen. Despite not being closely related, the white-breasted nuthatch and the white wagtail are very similar in plumage. The white-breasted nuthatch is a noisy bird. It has a nasal voice and often utters little cries or vocalizations, often composed of repetitions of small invariant whistles. In summer, it is an exclusively insectivorous bird, consuming a wide range of arthropods, but in winter its diet consists mainly of seeds. The nest is located in the cavity of a tree. The clutch consists of five to nine eggs, incubated for two weeks by the female, who is fed by the male. The two adults then feed the young until they fledge, and for a few weeks after that.

The white-breasted nuthatch breeds throughout much of North America, except in the cooler and drier areas. It is mainly found at low altitudes, in deciduous forests or in mixed woodlands. Seven to nine subspecies are generally distinguished by their slightly distinct distributions, vocalizations, and coloration. The species was once thought to be related to the white-cheeked nuthatch (S  leucopsis) and Przewalski's nuthatch (S. przewalskii), two species from southern Asia, but is actually more closely related to the giant nuthatch (S. magna), also from Southeast Asia. The species enjoys a very wide distribution and its population is said to be increasing; the International Union for the Conservation of Nature therefore considers it to be of "least concern."