Some sources believe that the population found in the western United States should be considered a distinct species and given the scientific name Martes caurina.

The marten lives in mature coniferous or mixed forests in Alaska and Canada, and south through the Rocky Mountains. Trapping and destruction of forest habitat have reduced its numbers, but it is still much more abundant than the larger fisher. The Newfoundland subspecies of this animal (Martes americana atrata) is considered to be endangered.

The American Marten has a long slender body covered in glossy brownish fur with a lighter coloured throat, a long bushy tail and a pointed snout. Like those of cats, its claws are semi-retractable, and aid it in climbing trees. It also has very large foot pads in relation to body weight allowing it to walk on hard snow. This provides the marten with a distinct advantage in areas that receive heavy snows.

The animal is omnivorous, preferring to catch and eat small mammals, especially the American Red Squirrel (Tamiasciurus hudsonicus), but readily consuming fish, frogs, insects, carrion, and fruit and other vegetation when available. It is most active at night, early morning, and late afternoon. It is usually solitary outside of the mating season. Males defend a territory of one to three square miles, and can be very aggressive toward other males. Mating occurs during the summer, but implantation of the fertilized egg is delayed (delayed implantation) and 1 to 5 young "kits" are born the following spring in a den in a hollow tree or rock cavity.