They are mostly marine fish found throughout the world and the vast majority are found in temperate or colder regions (tropical species are typically deep-water) while a few species may enter brackish estuaries.

Pacific tomcods, one of the two species that makes up the genus Microgadus, are able to enter freshwater, but there is no evidence that they breed there.

Some populations of landlocked Atlantic tomcod on the other hand, complete their entire life cycle in freshwater.

Gadiform fish range in size from the codlets, which may be as small as 7 cm (2.8 in) in adult length, to the Atlantic cod, Gadus morhua, which reaches up to 2 m (6.6 ft).

[3] The earliest gadiforms are Palaeogadus weltoni from the Maastrichtian of the United States and the undescribed, informally named "Protocodus" from the Early Paleocene of Greenland.