The National Archives and the regional state archives often welcome people searching for their ancestors to their reading rooms. Church books, censuses and other documents kept here give valuable information in the genealogical research.
Before visiting the archives you must collect all possible information about your ancestors in your local community. You can also visit The Digital Archives where you will find church books and censuses. Although the data will be in Norwegian, the service is also in English. Other digitized data may also be helpful, for example immigration lists for your home country.
Important facts are
You can write to the National Archives or the appropriate regional archives asking whether there are any further possibilities for information in the documents kept there.
You should, however, notice that these institutions are chiefly responsible for preserving the records and making them available for research use. The archives are not obliged to make extensive searches for the public, nor are they staffed to do so.
But you will always receive some help, or the archives will forward your inquiry to the appropriate agency. If possible, the archives will try to advise you how to proceed your work.
Lengthy genealogical inquiries, tracing lineages, construction of family trees, etc. must be pursued privately by a private genealogist. The archives can give you information about web sites with lists of investigators willing to accept private commissions, but will not be responsible for their results. Payment for private investigation is nearly always by the hour. As such work is generally very time-consuming, it is difficult to forecast how much time it will take. A fixed price per person or generation or similar arrangements are out of the question. Those commissioning such inquiries should specify at the outset the maximum sum they are prepared to spend.
If you visit Norway personally, you can study the documents in the archives, and the staff will, within reason, help and advise you. As you will have to do the research yourself, you will have to be able to read Norwegian (or, as far as the older records go, Danish) and also, in most cases, be able to decipher the old "Gothic" (German) style of lettering which was used in Norway until late in the 19th century.