Firs are evergreen coniferous trees belonging to the genus Abies in the family Pinaceae. There are approximately 48–65 extant species, found on mountains throughout much of North and Central America, Eurasia, and North Africa. The genus is most closely related to Keteleeria, a small genus confined to eastern Asia.

They are large trees, reaching heights of 10–80 meters (33–262 feet) tall with trunk diameters of 0.5–4 m (1 ft 8 in – 13 ft 1 in) when mature. Firs can be distinguished from other members of the pine family by the way in which their needle-like leaves are attached singly to the branches with a base resembling a suction cup, and by their cones, which, like those of cedars, stand upright on the branches like candles and disintegrate at maturity.