Lutefisk is made from dried (*not* salted) codfish called stockfish. Italian bacalao is also made of such stockfish. Spanish and Portuguese bacalao is made of dried and salted fish called klipfish. I'll explain a bit more in detail.
Every year, in the time from February to April, large quantities of Arctic cod will find themselves in the Vestfjord, South of the Lofoten archipelago, with a single purpose: copulation. This, of course, means that a lot of fishermen come to Lofoten at this time too, and the Lofoten Fisheries is a big event, and large quantities of codfish are landed.
Of course, all that codfish needs to be preserved some way - fresh fish does not last for long, unless it is frozen, or salted, or otherwise treated. These days, quite a lot of the codfish is frozen for the Norwegian market, and some is sold fresh, but most of it is still dried the old way.
Lofoten is blessed with a climate that is perfect for outdoors drying of codfish. They have tried to replicate the method at Iceland and in Finnmark, but the results are nowhere near as good. The method is quite simple - you take the cod (after having bled it, and removed head and guts) and hang it outdoors for a few months, until early summer, when it is dried. One hangs stockfish on something we call a fiskehjell, and there are generally two designs seen - one is the cathedral-like type, as seen at this page (the vertical distance between the horisontal stocks is round 3-4 feet), the other is lower and flatter, as can be seen in this image (incidentally from where I grew up (I've walked our late dog there many a time) and part of a Canadian student's entertaining tale of his escapades in Northern Norway while on an IAESTE summerjob in Tromsø - see the whole of it here). The horisontal wooden posts from which the stockfish is hung,a re called stocks, hence the name stockfish.
There are two qualities of stock-fish: råskjær (raw-cut) and rundfisk (round-fish). Råskjær refers to fish that, after having head and guts removed and while still raw, is split in two along the length of its spine, *almost* all the way up to the tail, where the two parts are left attached to eachother. You then simply hang this over the stocks by the tail. Round-fish refers to fish that has had head and guts removed (which would qualify it for a seat in Parliament), but has not been split - the fish are then tied together two and two with a piece of string around the tails, before being hung up to dry (as seen here (click on the arrow pointing right for more photos), part of this page on stockfish in Italy).
Stockfish will be collected from the hjells no later than the middle of June; it is important to get it in before the weather gets too warm, and flies and other insects start laying eggs in it. The stockfish is kept safe from seagull by deploying a pole with plastic falgs, streamers, emtpy plastic-bags or other things which flutter and make a lot of noise.
Stockfish is sorted into three primary qualities - Prima, Sekunda, and Afrika - and beyond that there are multitudes of type-variations, depending on size, shape, aroma, and so on. 90% of the stockfish is exported, the majority going to Italy, and stockfish contitutes the largest Norwegian export after crude-oil. Of the stockfish not exported to Italy, most is exported to Nigeria, this normally being the cheap stockfish of the lower qualities.
Stockfish can be used for food in a number of ways. One way is as a snack, simply tearing off small bits, and snacking oon it, as you would snack on crisps or pretzels - this is supposed to be good with beer, though I do not drink beer, and I'm not that crazy about straight stockfish either, so I wouldn't know. Soaking the stockfish in water for a while (I think two days) will return it to a state not far from that of fresh fish, and it can then be cooked as regular fish. It can also be used to make bacalao casserole, which is popular in Italy.
Finally, there is lutefisk. To make it into lutefisk, you start by soaking it in water, and then you immerse it in lye (we call it "to lye the fish"), and then you rinse the lye out (you "water out the fish"). Depending on how hard you lye and water out the fish, it will have different looks - hard-lyed fish cannot be boiled in water (it dissolves), but must be baked in an oven, and resembles nothing so much as a pale yellow gelatinous blob. More lightly lyed lutefisk will be more recognisable as fish, with colours ranging from white with only a hint of yellow (almost pearly), to a more pale yellowish hue. Traditionally, lutefisk is to be served with potatoes, bacon, creamed green peas, mustard, and often bechamel sauce. In my family, that is not how we serve it - my father didn't like those sides much when he was a kid, so his mother made it with proper mashed potatoes (and I mean *proper* - boiling potatoes, then adding butter and cream, and mashing by hand, with the result still tasting like real potatoes, and with small whole pieces of potatoes - not like that puree-like stuff most reastaurants will squirt out on your plate) - so that's how we have it.
Before being processed to stockfish, guts and heads are removed. The guts are not usable, and current regulations require that the guts are disposed of at approved disposal-sites to prevent pollution (these regualtions haveing been introduced by the EU through the EEA-agreement between EU and EFTA, which generally obliges the EFTA nations to honour EU directives). This is a slight problem, as, during the past 2-3 millennia, the seagulls have come to rely on the guts thrown out of the fishing-boats by the fishermen, so the seagulls are now starving - and the seagulls effectively have prevent these fishguts from presenting any actual pollution in all those thousands of years. The direct practical effect this has on the local population is that when you barbecue, you need to bring an object the general size and shape of a rifle, to keep the seagulls from diving down and snatching food right off the barbecue.
The heads, unlike the guts, can be used. I know there are parts in Norway where boiled (fresh) codfish-head is considered a delicacy worthy the Christmas Eve dinner-table. Thankfully I was not brought up in such a part of Norway. Codfish-heads in general are dried. The heads are tied together in a bundle with string, after the tongues have been cut out (to leave a hole so the string can be threaded through), and the particular business-arrangement surrounding this is a tale of its own (see below).
When the codfish-heads are good and dry (and they are, obviously, less carefully monitored than the stockfish), they can be used in a number of ways. Grounding it up to make fishflour is one possibility - this powder (with a pungent odour) can be used as fertiliser, to feed livestock or fish in fishfarms, or it can be used as an additive (used sparingly!) in regular food. But dried codfish-heads are also exported whole, primarily to Africa (Nigeria being a big taker), where they are used to cook soup.
Beyond stockfish, there is klipfish. Klip-fish derives it name from the verb "klippe", which refers to opening the fish (i.e., after you remove the head and guts, you cut the fish open along the underside so you can spread it out open). Klipfish is then salted and dried, and then stored, going through a form of curing while being stored. Klipfish when finished looks like roughly triangular pieces of stiff off-white parchment. Klipfish is exported in large quantities to Spain, Portugal, Brazil, Italy and France,a s well as amny other countries. The Spanish variant of bacalao uses klipfish rather than stockfish. See images from the klipfish-factory of the restaurant Havets Helter at Kræmmervika Rorbuer at Ballstad in Lofoten.
Essentially, the whole business of codfish-tongues could be seen as a form of childlabour, but that is really a bit inaccurate. What happens is that kid (below the age of confirmation - i.e. less than 15 years old) will take on the tying together of the codfish-heads, but in return they get the right to cut the tongues out, and they get ownership of the tongues. They then package the tongues in plastic bags in quantities of 1 kg (2.2lbs), and sell it at a price of NOK25 (ca. US$3) per kg. Thrifty kids have been known to make as much as NOK 70,000 (US$9,000) this way, in the process of a couple of months. The kids essentially negotiate a business-agreement with the owners fo the fishing-boats, rendering service, and being paid in the right to the tongues and the income therefrom. Traditionally, kids are not allowed to do this after they have reached the age of confirmation (going through confirmation being seen as a sign one is a grown-up), though lately, pensioners that are ahrd of money have been seen moving into tongue-cutting - but that is frowned upon by most people, and seen as susurping something that really is the kids' privilege. Not all kids do it (I didn't), and there is nothing compulsory about it. This is most common in Lofoten, but I believe you can find it elsewhere along the coast of Northern Norway as well.
The normal mdoe of preparing codfish-tongues is to fry them, and serve them with potatoes and normally squeeze some lemon over them, but some prefer a dab of melting butter. I have, however, been told of one alternative way of serving them, to which Tom, a friend of mine, was subjected. To understand this, I first must tell of fårikål. Fårikål essentially is mutton-chops, cooked for a few hours with cabbage and seasonings (you put water in a casserole, and then add layers of cabbage-leaves and mutton-chops, and add whole black pepper, tomato, slices of bell-pepper, etc., and cook it - third time recooked has the best taste, so in this case leftovers are actually better than the original).
Tom and his parents were having dinner at his grandmother's, as they'd do every Tuesday, and he thought she was serving fårikål (it certainly looked like it), and as he loves fårikål, he piled it on his plate. That was when he, to his great dismay, realised that it was not mutton that was intermingled with the cabbage on his plate - it was codfish-tongues! He braved the meal however - you do not lightly push away the dinner-plate when your grandmother cooked the dinner, after all - particularly not when it was you yourself who piled the food high on the plate. According to Tom the tongues were comparable to chewed-out chewing-gum, with a micture of fish- and cabbage-flavour.
Lefse, in Norway, normally does not involve potatoes these days. Lefse is a large collective term, for a number of unleavened normally soft cake- and bread-equivalents, made with wheat, barley, oat, or potatoes. Today, potato-lefse is primarily known as lompe in Norway, and is most commonly used to wrap a hotdog instead of a bun, though it can on occasion be seen eaten as a regular lefse. Most lefse seen in Norway today is wheat-based, however, and can be found in *countless* varieties, and are used as cakes. There are those that will eat lefse to certain types of dinner, though, including, but not limited to, lutefisk. I am not certain just what types of lefse is used here, and I won't treat this in much detail. Indeed I suspect the everyday-lefse as a staple of everyday diet is more known (though as a food for festive events) among US descendants of Norwegian emigrants than in Norway these days.
Lefse used as cake, has a number of common themes. Each lefse is made from a small piece of dough, rolled with a rollingpin until it is generally round, and rather thin, and then lightly baked on a griddle. Mørlefse is an exception to this, btw. It is then spread with butter, sugar, and cinnamon (either by spreading the butter, and sprinkling sugar and cinnamon over, or by mixing butter, sugar and cinnamon, and spreading the mixture), and is then folded together, just how (and if - there are again exceptions) depending on the type of lefse.
Regional variations include (and this is a very short list of only the very basics) Nordlands-lefse, which is pale, almost white, creamy, and positively delicious; mørlefse, which is rather thick and baked in a different way, and is rather filling; blanklefse, where one side of the lefse has been treated with a sourmilk-based mixture before baking causing it to be shiny - the filling is not applied until shortly before serving; krinalefse (aslo called kling), where, during baking, a batter is applied to one side and a decorative pattern made in it with a fork, the pattern setting during baking, and being folded so the pattern is on the outside; Vestlands-lefse, which is thicker and less delicate than many other types of lefse, and is often rolled up rather than folded; and straightforward everyday wheat-lefse of the sort that can be found in most grocery-ships, baked relatively small, only folded once, and cut in triangles.