see text Eels are ray-finned fish belonging to the order Anguilliformes (/æŋˈɡwɪlɪfɔːrmiːz/), which consists of eight suborders, 20 families, 164 genera, and about 1000 species.

The maximum size of this species has been reported as reaching a length of 3 m (10 ft) and a weight of 110 kg (240 lb).

[8] Some individuals of anguillid elvers remains in brackish and marine areas close to coastlines,[13] but most of them enter freshwater where they travel upstream and are forced to climb up obstructions, such as weirs, dam walls, and natural waterfalls.

Gertrude Elizabeth Blood found that the eel fisheries at Ballisodare were greatly improved by the hanging of loosely plaited grass ladders over barriers, enabling elvers to ascend more easily.

These early eels retain primitive traits such as pelvic fins and thus do not appear to be closely related to any extant taxa.

Body fossils of modern eels do not appear until the Eocene, although otoliths assignable to extant eel families and even some genera have been recovered from the Campanian and Maastrichtian, indicating some level of diversification among the extant groups prior to the Cretaceous-Paleogene extinction, which is also supported by phylogenetic divergence estimates.

One of these otolith taxa, the mud-dwelling Pythonichthys arkansasensis, appears to have thrived in the aftermath of the K-Pg extinction, based on its abundance.

[39] A traditional east London food is jellied eels, although the demand has significantly declined since World War II.

In northern Germany, the Netherlands, the Czech Republic, Poland, Denmark, and Sweden, smoked eel is considered a delicacy.

Katz (1998) identifies a number of Indo-European cognates, among them the second part of the Latin word for eels, anguilla, attested in its simplex form illa (in a glossary only), and the Greek word for "eel", ἔγχελυς enkhelys (the second part of which is attested in Hesychius as elyes).

[52][53] According to this theory, the name Bellerophon (Βελλεροφόντης, attested in a variant Ἐλλεροφόντης in Eustathius of Thessalonica) is also related, translating to "the slayer of the serpent" (ahihán).

The daylight passage in the spring of elvers upstream along the Thames was at one time called "eel fare".

Eel fishing in Nazi-era Danzig plays an important role in Günter Grass' novel The Tin Drum.

Sinister implications of eels fishing are also referenced in Jo Nesbø's Cockroaches, the second book of the Harry Hole detective series.

The 2019 book The Gospel of the Eels by Patrick Svensson commented on the 'eel question' (origins of the order) and its cultural history.