Eusthenopteron (from Greek: εὖσθένος eûsthénos 'stout', and Greek: πτερόν pteron 'wing' or 'fin') is an extinct genus of prehistoric marine lobe-finned fish known from several species that lived during the Late Devonian period, about 385 million years ago. It has attained an iconic status from its close relationship to tetrapods. Early depictions of animals of this genus show them emerging onto land, but paleontologists now think that Eusthenopteron species were strictly aquatic animals, though this is not completely known.

The genus was first described by J. F. Whiteaves in 1881, as part of a large collection of fishes from Miguasha, Quebec, Canada. Some 2,000 Eusthenopteron specimens have been collected from Miguasha, one of which was the object of intensely detailed study and several papers by paleoichthyologist Erik Jarvik between the 1940s and the 1990s. Further species have been described from other parts of Canada and northern Europe, indicating that this genus had a wide distribution.

Eusthenopteron is placed in the family Tristichopteridae, which has also been alternatively named Eusthenopteridae after this genus. It is related to genera such as Tristichopterus and Eusthenodon.

Eusthenopteron was widespread throughout what is now considered the Northern Hemisphere (which was located around the Equator at the time), and at least seven to eight species are known from Eurasia and North America. The following species list is based on Downs, Daeschler, Long & Shubin (2018):

The species E. wenjukowi was moved to its own genus, Jarvikina, in 1977 based on apparent morphological differences from Eusthenopteron, although this classification has been disputed. The species E. jenkinisi, described in 2018, indicates that Eusthenopteron may have been more morphologically variable than previously assumed, which further supports placing wenjukowi back in Eusthenopteron. The former species E. dalgleisiensis is now placed in its own genus, Heddleichthys.

Eusthenopteron is a medium- to large-sized tristichopterid. The species E. foordi is estimated to have exceeded 1.5 m (4 ft 11 in) in length, while the species E. jenkinsi probably reached 2.1 m (6 ft 11 in). Eusthenopteron may have weighed around 50 kilograms.

The earliest known fossilized evidence of bone marrow has been found in Eusthenopteron, which may be the origin of bone marrow in tetrapods.

It may have eaten smaller fish.