Cod is an ocean dwelling fish which prefers cold, deep waters such as those found in the Arctic. Cod has formed a staple part of the European diet for centuries, and is still popular in England and Portugal in fresh and salted forms, respectively. Like many other fish species, the survival of cod is uncertain due to overfishing, threats to the environment, and high levels of mercury bioaccumulation.

Many cod have barbels or whiskers on their faces which resemble large drooping mustaches. The cod also has a thrusting jaw and blunt head which cause the fish to look somewhat like a bulldog. Many cod are bottom dwelling, and eat small crustaceans and other fish. Cod can live to be 15 years of age and can weigh up to 66 pounds (30 kilograms), although cod of this size are extremely rare. Cod generally reach maturity and begin to breed at about six years of age, putting out large clouds of eggs which will hatch into young cod.

Cod was considered a major food fish for centuries, and was the building block of several nations including the United States, which turned a very large profit on preserved cod when it was a British colony. Cod has dense white flesh with minimal oil, which makes it ideal for preservation in salt, because it can be split, salted, and dried without danger of going rancid or rotting. Salted cod is extremely hard, and could be stacked into wagons for shipping all over Europe.

Salt cod is still popular in Portugal, where it is called bacalhau and used in many traditional dishes. Usually, salt cod is soaked before use to soften it and remove some of the salt. Salt cod is also common in the Caribbean, where it was introduced as a primary source of protein for slave populations. Many cultures fished for and salted cod, with the Basque people building the strongest cod based economy, trading salted cod for more salt with which to salt the next catch. Salt cod was also popular in Scandinavian cuisines, a welcome respite from the oily and sometimes putrid herring.

When fresh, cod is the traditional fish to use in English fish and chips, though the conservation status of the fish currently is such that it rarely occurs in fish and chips today. Atlantic cod is considered to be a threatened species by marine biologists, who encourage careful stewarding of cod fisheries and a severe reduction on commercial fishing. This has been devastating to small coastal fishing communities which relied on the cod for income, while commercial fishing corporations have simply drifted further to sea, further depleting cod stocks.

In the northern Pacific, ling cod is still commonly commercially fished, and is famous for reaching formidable sizes. Like Atlantic cod, the once plentiful species is at risk due to overfishing, with stocks growing small every year. More careful stewardship of cod fisheries in the Pacific has been recommended by marine conservation organizations to prevent the disappearance of the unique, yet endearing, fish.