The Martens constitute the genus Martes within the subfamily Mustelinae, in family Mustelidae. They are slender, agile, animals, adapted to living in taigas, and are found in coniferous and northern deciduous forests across the northern hemisphere. They have bushy tails, and large paws with partially retractile claws. The fur varies from yellowish to dark brown, depending on the species, and, in many cases, is valued by fur trappers. Martens are carnivorous animals related to wolverines, minks and weasels. Their diet consists of squirrels, mice, rabbits, birds, fish, insects, and eggs, and they will also eat fruit and nuts when these are readily available.
They are solitary animals, meeting only to breed in late spring or early summer. Litters of up to five blind and near-naked kits are born in early Spring. They are weaned after around two months, and leave the mother to fend for themselves at about three to four months of age.
Recent DNA research has shown that the genus Martes is in fact polyphyletic, placing Martes pennanti and Martes americana outside the genus and allying it with Eira and Gulo, to form a new New World clade. The genus first evolved up to seven million years ago, during the Pliocene.