US citizens do not need a visa to visit Norway for less than 90 days.
All foreign nationals who are to stay in Norway for more than 90 days must have a residence permit. Foreign nationals who are to work in Norway will in many cases need to have a residence permit, even for stays of less than 90 days.
You can find more information on visas and residence permits at the Norwegian Directorate of Immigration (UDI) website.
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