It is our traditional costume, made both for men, women and kids. They vary from place to place, over 200 versions are known, and it’s a very old tradition. The style varies from place to place, but it’s VERY time consuming to make, and it’s way too hot to wear in the summer. Usually it’s worn on our national/independence day (17th of May), weddings and other happy occasions.
You can see a great gallery of bunads here: http://www.norskflid.no/bunad/bunader/