Short Time Work
There are special immigration rules if you work for less than three months, and special tax rules for those working for less than three days.
Working Less than Three Months
Researchers and lecturers do NOT need a residence permit for work up to three months (in a year).
But some may need a visitor's visa to enter Norway.
Even if the general rule is that you cannot work while you are visiting Norway on a visitor's visa - researchers and lectures are a few of the exemptions.
You need documentation of the purpose of your visit to Norway, so you should get an invitation or have a contract with your employer. Your employer should give you an "Offer of employment" and if the visitor come from a country that can have difficulties to obtain a visa, we advice the employer to write a more extended invitation.
You need a tax deduction card if your work is performed in Norway. The first time you apply for the tax deduction card, you have to appear in person at the tax-office for id check and to apply for the card. Your application for the tax card will also be an application for ID number (or D number).
Working less than 3 days
It is possible to get exempted from the duty to appear in person at the tax office for lecturers in universities and colleges that are in the country for just a few days. So you may have worked more for UiB abroad, but not while you have been in Norway. An example of such is a member of a PhD-evaluation committee or a guest lecturer. In such cases, the department /unit needs to be notified (in advance) and can then register your employment on your behalf at the tax office.
NB - if you have worked in Norway for other employers, this will also be included when estimating number of days in Norway by the tax office.