Lutefisk (Norwegian) or lutfisk (Swedish) (pronounced [ˈlʉːtˌfesk] in Northern and Central Norway, [ˈlʉːtəˌfisk] in Southern Norway, [ˈlʉːtˌfɪsk] in Sweden and in Finland (Finnish: lipeäkala )) is a traditional dish of some Nordic countries. It is traditionally part of the Norwegian julebord and Swedish julbord.
Lutefisk is dried whitefish (normally cod, but ling and burbot are also used) treated with lye. The first step is soaking the stockfish in cold water for five to six days (with the water changed daily). The saturated stockfish is then soaked in an unchanged solution of cold water and lye for an additional two days. The fish swells during this soaking, and its protein content decreases by more than 50 percent, producing a jelly -like consistency.
When this treatment is finished, the fish (saturated with lye) is caustic, with a pH of 11–12. To make the fish edible, a final treatment of yet another four to six days of soaking in cold water (also changed daily) is needed. Eventually, the lutefisk is ready to be cooked.
In Finland, the traditional reagent used is birch ash. It contains high amounts of potassium carbonate and bicarbonate, giving the fish a more mellow treatment than wood lye. It is important not to marinate the fish too long in the lye because saponification of the fish fats may occur.
After the preparation, the lutefisk is saturated with water and must therefore be cooked extremely carefully so that it does not fall to pieces.
To create a firm consistency in lutefisk, it is common to spread a layer of salt over the fish about half an hour before it is cooked. This will "release" some of the water in the fish meat. The salt must be rinsed off carefully before cooking.
Lutefisk does not need additional water for the cooking; it is sufficient to place it in a pan, salt it, seal the lid tightly, and let it steam cook under a very low heat for 20–25 minutes. An alternative is to wrap in aluminium foil and bake at 225 °C (435 °F) for 40–50 minutes.
Lutefisk sold in North America may also be cooked in a microwave oven. The average cooking time is 8–10 minutes per whole fish (a package of two fish sides) at high power in a covered glass cooking dish, preferably made of heat resistant glass. The cooking time will vary, depending upon the power of the microwave oven.
When cooking and eating lutefisk, it is important to clean the lutefisk and its residue off pans, plates, and utensils immediately. Lutefisk left overnight becomes nearly impossible to remove. Sterling silver should never be used in the cooking, serving or eating of lutefisk, which will permanently ruin silver. Stainless steel utensils are recommended instead.
In Sweden and Finland lutefisk is a part of the Christmas tradition and is mostly eaten with boiled potatoes, green peas and white sauce. Regional variations include a sprinkle of freshly ground allspice or black pepper and the addition of coarsely ground mustard in the white sauce (in Scania). In parts of Jämtland it is served on flat bread along with whey cheese.
In the United States lutefisk is often served with a variety of side dishes, including: bacon, green peas, green pea stew, potatoes, lefse, gravy, mashed rutabaga, white sauce, melted or clarified butter, syrup, geitost, or "old" cheese (gammelost). It is sometimes eaten together with meatballs which is not traditional in Scandinavia. Side dishes vary greatly from family to family and region to region, and can be a source of jovial contention when eaters of different "traditions" of lutefisk dine together.
The taste of well-prepared lutefisk is very mild, and often the white sauce is spiced with pepper or other strong tasting spices. In Minnesota, this method (seasoned with allspice) is common among Swedish-Americans, while Norwegian-Americans often prefer to eat it unseasoned with melted butter or cream sauce.
An article in Smithsonian magazine quotes some oft-rendered tall tales regarding the origins of the dish:
No one is quite sure where and when lutefisk originated. Both Swedes and Norwegians claim it was invented in their country. A legend has it that Viking fishermen hung their cod to dry on tall birch racks. When some neighboring Vikings attacked, they burned the racks of fish, but a rainstorm blew in from the North Sea, dousing the fire. The remaining fish soaked in a puddle of rainwater and birch ash for months before some hungry Vikings discovered the cod, reconstituted it and had a feast. Another story tells of St. Patrick's attempt to poison Viking raiders in Ireland with the lye-soaked fish. But rather than kill them, the Vikings relished the fish and declared it a delicacy. It makes for a great story if you don’t mind the fact that Patrick lived centuries before the Vikings attacked Ireland.
The actual reason is probably that the lack of major salt deposits in the area favored the drying process for the preservation of whitefish - a process known for millennia. Stockfish is very nutrient-rich, and one can assume that it was also consumed domestically, although it was during the boom in the stockfish trade in the late Middle Ages, the product became accessible throughout Scandinavia, as well as the rest of Europe. The higher quality stockfish would be soaked in water, then boiled and eaten with melted butter. Lower grade qualities would be harder and more fuel consuming to boil and it has been suggested that adding ash from beech or birch in the boiling water, would break down the protein chains and speed up the process. The introduction of lye in the preparation process might therefore have been incidental. 
Lutefisk as a Christmas season meal has gained attention in Norway over the past 20 years.    The Norwegian Seafood Export Council indicated sales of lutefisk to restaurants and catering companies in Norway increased by 72% between 2005 and 2008.  A 2005 survey found 20% of Norwegians ate lutefisk during the Christmas holiday season, although only 3% would consider it for their Christmas dinner. 
Madison, Minnesota has dubbed itself the "lutefisk capital of the world" as well as claiming the largest per capita consumption of lutefisk in Minnesota.  St. Olaf College in Northfield, Minnesota serves lutefisk during their Christmas Festival concerts. They also host an annual music festival called "Lutefest". Lutefisk, though, is not served at this festival. 
Lutefisk is also consumed in Canada because of its relatively large Scandinavian population, particularly in Western Canada. There are about 450,000 Norwegian Canadians, 340,000 Swedish Canadians, 200,000 Danish Canadians and 136,000 Finnish Canadians. Organizations such as the Sons of Norway hold annual lutefisk dinners. Lutefisk is sometimes available in specialty stores  and supermarkets where there are large Scandinavian populations. Kingman, Alberta proclaims itself on its greeting sign to be the "Lutefisk capital of Alberta".
- Danish: ludfisk or ludefisk
- Norwegian: lutefisk (earlier ludefisk spelling still sometimes used in English) or lutfisk
- Swedish: lutfisk
- Finnish: lipeäkala or livekala
- Northern Sami: lovttaguolli