They are large trees, reaching heights of 10–80 m (33–262 ft) tall and 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 unique attachment of their needle leaves and by their different cones.
Identification of the different species is based on the size and arrangement of the leaves, the size and shape of the cones, and whether the bract scales of the cones are long and exserted, or short and hidden inside the cone.
Firs can be distinguished from other members of the pine family by the unique attachment of their needle-like leaves to the twig by a base that resembles a small suction cup.
The leaves are significantly flattened, even looking like they are pressed.
The leaves have two whitish strips on the bottom, each of which is formed by wax-covered stomatal bands. The upper surface of the leaves usually is uniformly green and shiny, without stomata or only with few at their tips, visible as whitish spots. Some of the species however have the upper surface of leaves dull, gray-green, bluish-gray to silvery, coated by wax with variable number of stomatal bands, and not always continuous. An example species with shiny green leaves is A. alba, and an example species with dull waxy leaves is A. concolor.
The tips of leaves are usually more or less notched, but sometimes rounded or dull or sharp and prickly. The leaves of young plants are always sharper.
The way they spread from the shoot is extremely diverse, only in some species comb-shaped, with the leaves arranged on two sides, flat.