The boreal owl was formally described by the Swedish naturalist Carl Linnaeus in 1758 in the tenth edition of his Systema Naturae.

[6][7] The genus name is Latin for a screech owl, the word came from the Ancient Greek aigōlios meaning "a bird of ill omen".

[9] Seven subspecies are recognized:[7] Remains of the boreal owl dating back to the Pleistocene era were found in a cave in southern New Mexico.

Its large head has yellow eyes and an olive-brown crown with small white droplets and larger central spots.

[14] Juvenile boreal owls, at about 3 weeks old, have a completely dull, chocolate-brown upperparts and underparts, with a dark brown facial disc bordered by black and white markings near the bill.

Upon fledging, their plumage remains similar but with white markings on the neck, scapulars, flight feathers, and tail.

[12] The Definitive Prebasic molt is also partial, affecting all of the head, body, and wing coverts, as well as the tail, but only a portion of the flight feathers, which are replaced in a specific order each year.

The preferred habitats are old-growth forests as they provide shelter from avian predators and an abundant number of preys.

[19] Breeding habitats include boreal forests of black and white spruce,[19] birch and aspen across northern North America and the Palearctic, and in mountain ranges such as the Alps and the Rockies.

However, northern populations may migrate south in response to snow depth and poor prey availability, but eventually return to their breeding grounds.

The breeding begins with a lengthy courtship process where males sing for up to 102 days, starting from mid-February to mid-April, depending on environmental factors like prey availability and weather.

[25][9] Breeding densities fluctuate based on prey availability, ranging from 0.6 to 26 nests per square kilometer across different regions.

Their extreme asymmetrical skulls leads to sound localization in both horizontal and vertical directions and allow them to capture preys under snow and dense vegetation.

[30] Logging activities have a negative impact on prey availability, foraging efficiency and suitable nesting sites.

[32] The slow forest succession in spruce-fir ecosystems disrupts the recovery of critical habitat which impacts the species' ability to thrive.

[19] The black woodpecker (Dryocopus martius) population decline in Eurasia has also led to a reduced number of nesting cavities.

[35] Moreover, nuthatches (Sitta europaea) have been observed blocking the entrance of nests with mud, occasionally trapping females inside and starving them to death.

Their appearance in art reflect a deep bond between humans and owls, based on shared environment and a strong "sense of place.