You do not need a visa if you are:
a citizen of an EU/EEA country. Free movement applies, and neither a visa nor a residence permit is required for entry. Source:
a national of a country listed in Annex II of Regulation (EU) 2018/1806, who is visa‑exempt for stays of up to 90 days in any 180‑day period.
a national of the United Kingdom for visits of up to 90 days in any 180-day period. Since Brexit, UK citizens require a residence permit for stays beyond 90 days, including work or long‑term residence. Specific UK guidance:
Visa‑exempt travellers may visit Norway for tourism, family visits, business meetings, cultural/sporting events or short training programmes.
You need a visa if you are:
a national of a third country not included in the visa‑exempt list under Regulation (EU) 2018/1806;
a holder of travel documents issued by entities or authorities not recognised as states by at least one EU Member State (e.g. Palestinian Authority, Kosovo as defined by UNSC Resolution 1244).
The official UDI tool allows applicants to select their nationality to verify whether a visa is required:
https://www.udi.no/en/want-to-apply/