The black-capped chickadee (Poecile atricapillus) is a small, nonmigratory, North American passerine bird that lives in deciduous and mixed forests. It is a member of the Paridae family, also known as tits. It has a distinct black cap on its head, a black bib underneath, and white cheeks. It has a white belly, buff sides, and grey wings, back, and tail. The bird is well known for its vocalizations, including its fee-bee song and its chick-a-dee-dee-dee call, from which it derives its name.

The black-capped chickadee is widely distributed throughout North America, ranging from the northern United States to southern Canada and all the way up to Alaska and Yukon. It feeds primarily on insects and seeds, and is known for its ability to cache food for use during the winter. The hippocampus of the black-capped chickadee grows during the caching season, which is believed to help it better remember its cache locations. The black-capped chickadee is a social bird and forms strict dominance hierarchies within its flock. During the winter, these flocks include other bird species. It has the ability to lower its body temperature during cold winter nights, allowing it to conserve energy.

Black-capped chickadees build nests in tree cavities, with the nesting season starting in late April and lasting until late June. They lay on average 6–8 eggs, which hatch after 11–14 days. Juveniles fledge 12–16 days after hatching.

The population of black-capped chickadees is thought to be increasing, and they are considered a species of least concern by the International Union for Conservation of Nature (IUCN). It is the state bird of both Massachusetts and Maine in the United States, and the provincial bird of New Brunswick in Canada.

In 1760, French zoologist Mathurin Jacques Brisson included a description of the black-capped chickadee in his book Ornithologie based on a specimen collected in Canada. He used the French name La mésange a tête noire de Canada and the Latin Parus Canadensis Atricapillus. Although Brisson gave it Latin names, these do not conform to the binomial system and are not recognised by the International Commission on Zoological Nomenclature. In 1766, Swedish naturalist Carl Linnaeus published the 12th edition of his Systema Naturae, which included 240 species that had been previously described by Brisson. One of these was the black-capped chickadee. Linnaeus included a brief description, coined the binomial name Parus atricapillus and cited Brisson's work. The specific epithet atricapillus is Latin for "black-haired" from ater (black) and capillus (hair of the head).

Though originally placed in the genus Parus with most other tits, mtDNA cytochrome b sequence data and morphology suggested that separating Poecile more adequately expressed these birds' relationships. The genus Poecile had been introduced by German naturalist Johann Jakob Kaup in 1829, and the American Ornithologists' Union moved the black-capped chickadee into this genus in 1998. Molecular phylogenetic studies have shown that the black-capped chickadee is sister to the mountain chickadee (Poecile gambeli).

The following cladogram shows the relationships between the various chickadee species, a subset of genus Poecile:

Until the late 1900s, the black-capped chickadee was considered by some to be conspecific with the willow tit of Eurasia and the Carolina chickadee, due to their very similar appearance. A 1989 study demonstrated that the Willow tit and black-capped chickadee were different species; however, the distinction of the Carolina chickadee remained in question until 2005.