The celebration of namnsdagar (name days) in Sweden is an old tradition that goes back to the Middle Ages. Originally it was a Catholic and Orthodox custom, but the Protestant Church retained certain Catholic habits, and celebrating name days was one of them. The namnsdagar originate in the holidays celebrated in commemoration of saints and martyrs to the Church. For example, the name Karl, or Carl, which is celebrated in Sweden on January 28, was originally Carolus Magnus, the Latin form of Charlemagne, who died on this date. The Church promoted celebration of namnsdagar (or rather saintsí feast days) over birthdays, as birthdays were seen as a Pagan tradition.
Namnsdagar today are being celebrated in many different countries and to various degrees. In some countries, like Poland and Greece, itís a festive celebration that involves presents, parties, and desserts. In Sweden (the only country in Scandinavia except Finland, that really celebrates namnsdagar), we usually donít go that far, although the lucky person might get a small treat, especially if itís a child.

An evolving list
As for what names are being celebrated in Sweden, well, that has been tampered with somewhat. From the 18th century on, names used by the royal family have been introduced to the Swedish list of namnsdagar, followed by other common names. In 1901 a comprehensive modernization was made to update the list with current names. The monopoly on almanacs, held by the Royal Swedish Academy of Sciences, expired in 1972 and so did the official list of name days. Competing lists began to emerge but the official list was still in general use until 1986, when consensus of a new list with three names on each day was reached. This list was revised in 1993 and reduced to two names on each day. However, widespread dissatisfaction with the list prompted the Swedish Academy to compile a new two-name list, which was finally accepted and brought into use in 2001. Although it does not have the official status of the 1901 or older lists, it is now universally used in Sweden.
If you'd rather read about learning Swedish in America, see http://www.nordstjernan.com/news/education/766/