American martens are in the Mustelidae family that includes weasels, sea otters, and even—the significantly larger—wolverines. American martens have short legs, black eyes, large, round ears, and curved claws that help them climb trees. Their bodies can grow to 14–17 in in length with a tail that is 7–9 in, and adults weigh 2–4 lbs. They typically have yellowish brown fur, with dark brown fur on their legs and tails along with a throat patch that is white or yellow. These largely nocturnal animals live a solitary lifestyle and are highly territorial. They feed on small mammals like pikas, chipmunks, and rabbits, and they can eat insects, berries, and parts of mountain ash trees.

Martens prefer mature coniferous or mixed-wood forests. These areas provide important prey habitat, protection from predators, and denning sites. They inhabit forests in Canada, Alaska, northern New England, the Great Lakes region, and the Rocky Mountain and Sierra Nevada mountain ranges. They prefer dense forests and tend to live on shore pines and fir trees. Trees are an essential part of their habitat because they build dens inside empty tree hollows. They can also shelter in burrows that other animals leave behind.