Norse religion refers to the religious traditions of the Norsemen prior to the Christianization of Scandinavia, specifically during the Viking Age.
Norse religion is a folk religion. It was the northern variation of the religion practiced in the lands inhabited by the Germanic tribes across most of Northern and Central Europe prior to Roman and Holy Roman incursions. However, it was not formalized nor categorized as a subset of Germanic paganism until it was described by outsiders who came into contact with native practitioners. Knowledge of Norse religion is mostly drawn from the results of archaeological field work, etymology and early written materials as it was largely a product of early practitioners who did not have a written history.
The Norse - or people of Scandinavia - have always had extensive contact with cultures outside Scandinavia, even in the earliest Stone Age. They were well aware of foreign religions (including Arianism). They traded, intermarried and sometimes worked as henchmen for other cultures, including the Romans. Most titles bestowed upon Norse religion are the ones which were used to describe the religion in a competitive manner, usually in a very antagonistic context. Some of these terms were hedendom (Scandinavian), Heidentum (German), Heathenry (English) or Pagan (Latin). A more romanticized name for Norse religion is the medieval Icelandic term Forn Siðr or "Old Custom".
Knowledge about Norse religion has been gathered from archaeological discoveries and from literature produced after the Christianization of Scandinavia.