Constitution Day is the national day of Norway.
It is observed on May 17 because the Norwegian Constitution was signed on May 17, 1814.
The constitution declared Norway's independence.
In 1814, Denmark–Norway was defeated in the Napoleonic Wars.
Norway declared its independence in order to avoid being ceded to Sweden (ironically, it entered into a union with Sweden later that year).
For some years during the 1820s the holiday was actually banned because it was believed to threaten the union.
In 1829, King Charles XIV John allowed the celebration of Constitution Day, but the first official celebration was held in 1833.
After the dissolution of the union, the holiday also began to honor the Norwegian Royal Family.
Constitution Day is an official flag flying day in Norway.