Norwegian Naming Practices
Patronymics - the surname of the child is the first name of the
father with either 'sen' (son) or 'datter, dtr' (daughter) following it.
Example: Hansen (son of Hans) or Hansdatter (dau of Hans)

Fixed surnames: Nobility, townsmen, merchants, tradesmen,
and clergy used fixed surnames much earlier than the common
classes of people, until the late 1800's.

Farm names: Use of the farm name was not technically a legal
part of a person's name, it was used to help identify a person.
Lars Nielsen, living on the farm Brevig would be known as Lars
Nielsen Brevig or Lars Brevig. If Lars Nielsen moved and the
farm was named Lona, he would become Lars Nielsen Lona. It is
important to note that many Norwegian immigrants to the US
retained their farm names as their permanent surname in the
Untied States. This is one of the best clues for finding the family
location in Norway.

Trade names: Sometimes skilled craftsmen used their  
occupation as a surname. Lars the shoemaker (Skomager)
became Lars Skomager; Hans the tinsmith (Tindstobe), became
Hans Tindstobe.

Illegitimate Children's names: There was no set rule. Often if
the father's name was known the name followed standard
patronymic patterns. If the father was not known, the child may
not have a recorded surname until leaving home or marrying.

Naming Customs: it was common practice to name the first
children after their grandparents. The first two boys would be
named after the paternal then maternal grandfathers, the first
two daughters would be named after the paternal then maternal
grandmothers. In certain instances, such as when both male
grandparents have the same given name, this practice led to
having more than one child with the same given name in a single
family unit.