Stockfish is unsalted fish, especially cod, dried by sun and wind on wooden racks on the foreshore called flakes, or in special drying houses. 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.
Cod is the most common fish used in stockfish production, while other whitefish, such as pollock, haddock, ling and tusk, are used to a lesser degree. Over the centuries, several variants of stockfish have evolved, notably salt cod (q.v.). Salting was not economically feasible before the 17th century, when cheap salt from southern Europe became available to the maritime nations of northern Europe.