Stockfish is unsalted fish, especially cod, dried by cold air and wind on wooden racks (which are called "hjell" in Norway) on the foreshore. The drying of food is the world's oldest known preservation method, and dried fish has a storage life of several years. The method is cheap and effective in suitable climates; the work can be done by the fisherman and family, and the resulting product is easily transported to market.

Over the centuries, several variants of dried fish have evolved. The stockfish (fresh dried, not salted) category is often mistaken for the klippfisk, or salted cod, category where the fish is salted before drying. Salting was not economically feasible until the 17th century, when cheap salt from southern Europe became available to the maritime nations of northern Europe.

Stockfish is cured in a fermentation process where cold-adapted bacteria matures the fish, similar to the maturing process of cheese.

In English legal records of the medieval period, stock fishmongers are differentiated from ordinary fishmongers when the occupation of a plaintiff or defendant is recorded.

The word stockfish is a loan word from West Frisian stokfisk (stick fish), possibly referring to the wooden racks on which stockfish are traditionally dried or because the dried fish resembles a stick. "Stock" may also refer to a wooden yoke or harness on a horse or mule, once used to carry large fish from the sea or after drying/smoking for trade in nearby villages. This etymology is consistent with the fact that "Stockmaß" is German for the height of a horse at the withers.^{[citation needed]}

Stockfish is Norway's longest sustained export commodity. Stockfish is first mentioned as a commodity in the 13th-century Icelandic prose work Egil's Saga, where chieftain Thorolf Kveldulfsson, in the year 875 AD, ships stockfish from Helgeland in mid-Norway to Britain. This product accounted for most of Norway's trade income from the Viking Age throughout the Medieval period.

Preserved cod fed Iceland for centuries, to the extent that it has been described as a local equivalent of bread.

Stockfish is extremely popular and is widely consumed in Catholic Mediterranean countries, mostly in Italy. (Stockfish is called stoccafisso in most Italian dialects, but confusingly baccalà—which normally refers to salt cod—in the Veneto). In Russian cuisine dried stockfish is a very popular dish which is often eaten with vodka and beer. In the 16th century Russian and Swedish stockfish were sold to many European countries.