Norse Paganism organized its gods into two related families: the Aesir, led by Odin, god of war, wisdom and the dead, and including Thor, Tyr, Frigg, Baldr and Heimdall; and the Vanir, fertility deities including Freyja, Freyr and Njord, who joined the Aesir in Asgard after a mythic war between the two tribes. Cosmology set nine worlds around the world tree Yggdrasil, among them Asgard (home of the gods), Midgard (the human world) and Helheim (a realm of the dead), with Valhalla, Odin's hall, receiving warriors chosen in battle by his valkyries. Almost everything known of this system comes from Iceland two centuries after conversion: the Prose Edda, a handbook of poetic technique and myth compiled around 1220 by the Christian chronicler and politician Snorri Sturluson, and the anonymous Poetic Edda preserved in the thirteenth century Codex Regius manuscript.
That gap between practice and record is a live methodological problem. Rudolf Simek's Dictionary of Northern Mythology and John Lindow's Norse Mythology: A Guide both caution that Snorri, writing as a Christian antiquarian rather than a believer, likely systematized and in places invented connective material to make disparate oral poems read as one coherent mythology, so scholars weigh Eddic material against skaldic verse, place names and archaeology rather than treating Snorri as a neutral transcript of pagan belief. The Elder Futhark runic alphabet, twenty four characters used for memorial inscriptions and, tradition holds, divination and magic, is the one Norse Pagan-era writing system to survive in its own words. No unbroken pre-Christian practice survives; the modern Heathenry or Asatru revival, active since the twentieth century, reconstructs Norse Pagan worship from these same sources.