In pretty much all countries in the world, people have names. Using names are a great way to make it easier for people to understand you are talking to or about them in conversations. Names also make it easier to identify someone when looking for additional information in a data base.
Swedes don't have a large pool of last names or first names to choose from, for example many are called Johan Andersson or Anna Johnsson. Since many Swedes have identical names, they can easily get confused with each other. This is why Sweden introduced the personnummer-system.
Swedish personnummer, personal identity number
Every Swede gets a personal identity number. Those numbers are issued by Skatteverket, the Swedish Tax Agency, as part of the population register.
A personal number can look like this: 911228-3244
Ten digits which represent your birthday and four extra digits. In the example above: year '91, month December (12), day 28th, and the last four digits
The last four digits are determined partly by the place of your registration (usually where you're born in Sweden), your gender and the last digit is the result of some kind of weird algorithm which is really hard to explain in short, read here.
Use your personnummer
As soon as you, dear new-Swede, have received a personnummer, it's time to learn it by heart. Actually you don't have to put too much effort into learning your number since you will have to repeat it so many times in your life in Sweden, that it's difficult not to remember it.
Since even companies can request personal information from Skatteverket about you, like for example your address, you might simply be asked for your personal identity number when you order something on the internet, sign a mobile phone contract or book an appointment at your car workshop.
Here is how to get a Swedish personal identity number/card
So, dear new-Swede, if you haven't yet, it's time to apply for your personnummer. The one with the coolest four extra digits wins.