There are two types of identification numbers in Norway, a national identity number (fødselsnummer) and D number.
A Norwegian identity number (fødselsnummer) is given by the National Population Register if you meet the requirements and cannot be applied for. It will be issued to all who are born in Norway, persons that moves to Norway and Norwegian citizens born abroad that needs it to get a Norwegian passport.
D number is a Norwegian identification number for foreigners with a temporary connection to Norway. You may be issued a D number if you plan to stay in Norway for less than 6 months, or more than 6 months, but you don’t meet the conditions for being assigned a national identity number. To receive a D number some public agencies or enterprises can order it for you. For example, if you apply for a tax deduction card, the Tax Administration will order a D number.
Other examples are if you are working or carrying out business activity, are an asylum seeker or have another form of valid residence permit, receive national insurance contribution from Norway, are a board member in an enterprise or own a residential property.
Usually, the enterprise that orders a D number for you requires an identity verification. You will then have to book an appointment with the Tax Administration and undergo an ID check in person.
The D number is active for 5 years. After this its status will be inactive, but it is still valid and will not be deleted. If you need to activate it again you need to have an appointment with the Tax Administration.
If you intend to stay in Norway for more than six months consecutively, you must report a move to the National Population Register. You must undergo an ID check and provide documentation that you’ll be living in Norway for at least 6 months. It is the National Population Register that will determine if you meet the conditions and you will be given a Norwegian identity number (fødselsnummer). If you’ve been granted a residence permit from the immigration authorities, they will usually report the move for you.