The beech marten (Martes foina), also known as the stone marten or white breasted marten, is a species of marten native to much of Europe and Central Asia, though it has established a feral population in North America. It is listed as Least Concern by the IUCN on account of its wide distribution, its large population, and its presence in a number of protected areas. It is superficially similar to the pine marten, but differs from it by its smaller size and habitat preferences ; while the pine marten is a forest specialist, the beech marten is a more generalist and adaptable species, occurring in a number of open and forest habitats.

Its most likely ancestor is Martes vetus, which also gave rise to the pine marten. The earliest M. vetus fossils were found in deposists dated to the Würm glaciation in Lebanon and Israel. The beech marten likely originated in the Near East or southwestern Asia, and may have arrived in Europe by the Late Pleistocene or the early Holocene. Thus, the beech marten differs from most other European mustelids of the Quaternary, as all other species (save for the European mink) appeared during the Middle Pleistocene. Comparisons between fossil animals and their descendants indicate that the beech marten underwent a decrease in size beginning in the Würm period. Beech martens indigenous to the Aegean Islands represent a relic population with primitive Asiatic affinities.