There are thirteen Student Nations in Uppsala. They date back to the 17th century. A Student Nation is a kind of club for students from a certain region in Sweden. The Nations organise a lot of different activities and they all have pubs and restaurants for students with comparatively low prices. They also provide housing and have small libraries.
Foreign students are free to join any Nation they like.
It is, however, compulsory to be a member of a Nation, and you have to pay a fee of 200 SEK per semester. The student ID allows you to visit the Nations and you must always remember to bring it to exams. There is a fourteenth Nation, Sk nelandens Nation , which only requires a very small fee, but has no facilities or activities. If you register with this nation you will not be admitted to the other nations and cannot, for instance, use the University Library without a deposit fee. But as a member of this nation you will be allowed to take exams.