Population registration & obtaining a personal identity number
If you are planning to stay in Sweden for more than 12 months, you will need to register at the Swedish Tax agency (called population registration). Note that you need to have an address before you can register.
After registering with the Tax agency, you will recieve a Swedish personal identity number (personnummer). Everyone registered in Sweden has a personal identity number, and you will need one before you can become part of the Swedish system. This number is unique to each individual, is based on your date of birth, and follows you throughout your life. It is used for identification in many everyday situations so it is a good idea to learn it by heart.