In Norse mythology, the Æsir–Vanir War was a conflict between two groups of deities that ultimately resulted in the unification of the Æsir and the Vanir into a single pantheon. The war is an important event in Norse mythology, and the implications for the potential historicity surrounding accounts of the war are a matter of scholarly debate and discourse.

Fragmented information about the war appears in surviving sources, including Völuspá, a poem collected in the Poetic Edda in the 13th century from earlier traditional sources; in the book Skáldskaparmál in the Prose Edda, written in the 13th century by Snorri Sturluson; and in euhemerized form in the Ynglinga saga from Heimskringla, also written by Snorri Sturluson in the 13th century.

The following attestations provide information about the war:

In two stanzas of Völuspá, the war is recounted by a völva (who refers to herself here in the third person) while the god Óðinn questions her. In the first of the two stanzas, the völva says that she remembers the first war in the world, when Gullveig was stabbed with spears and then burnt three times in one of Óðinn's halls, yet that Gullveig was reborn three times. In the later stanza, the völva says that they called Gullveig Heiðr (meaning "Bright One"^[1] or potentially "Gleaming" or "Honor"^[2]) whenever she came to houses, that she was a wise völva, and that she cast spells. Heiðr performed seiðr where she could, did so in a trance, and was "always the favorite of wicked women."^[1]

In a later stanza, the völva then tells Óðinn that all the powers went to the judgment seats and discussed whether the Æsir should pay a fine or if all of the gods should instead have tribute. Further in the poem, a stanza provides the last of the völva's account of the events surrounding the war. She says:

These stanzas are unclear, particularly the second half of stanza 23, but the battle appears to have been precipitated by the entry of Gullveig/Heiðr among the Æsir.^[3] Stanza 23 relates a difficulty in reaching a truce which led to the all-out war described in stanza 24. However, the reference to "all the gods" could, in Lindow's view, indicate a movement towards a community involving both the Æsir and the Vanir.^[3] Ursula Dronke points to extensive wordplay on all the meanings of the gildi and the adjective gildr to signal the core issue of whether the Æsir will surrender their monopoly on human tribute and join with the "all-too-popular" Vanir; as their only alternative, they attack again.^[4]

In the Prose Edda book Skáldskaparmál (chapter 57), the god Bragi explains the origin of poetry. Bragi says that it originated in the Æsir–Vanir War, when during the peace conference the Æsir and the Vanir formed a truce by all spitting into a vat. When they left, the gods decided that it should not be poured out, but rather kept as a symbol of their peace, and so from the contents made a man, Kvasir. Kvasir is later murdered, and from his blood is made the Mead of Poetry.^[5]

In chapter 4 of Heimskringla, Snorri presents a euhemerized account of the war. The account says that Óðinn led a great army from Asia ("Asgard") to attack the people of "Vanaheim." However, according to Snorri, the people of Vanahiem were well prepared for the invasion; they defended their land so well that victory was up for grabs from both sides, and both sides produced immense damage and ravaged the lands of one another.^[6]

The two sides eventually tired of the war and both agreed to meet to establish a truce. After doing so, they exchanged hostages. Vanaheim is described as having sent to Asgard its best men: Njörðr—described as wealthy—and his son Freyr in exchange for Asgard Hœnir—described here as large, handsome, and thought of by the people of Vanahiem well suited to be a chieftain. Additionally, Asgard sends Mímir—a man of great understanding—in exchange for Kvasir, who Snorri describes as the wisest man of Vanahiem.^[6]

Upon arrival in Vanahiem, Hœnir was immediately made chief, and Mímir often gave him good counsel. However, when Hœnir was at meetings and at the Thing without Mímir by his side, he would always answer the same way: "Let others decide." Subsequently, the Vanahiem folk suspected they had been cheated in the exchange by the Asgard folk, so they seized Mímir and beheaded him and sent the head to Asgard. Óðinn took the head of Mímir, embalmed it with herbs so that it would not rot, and spoke charms over it, which gave it the power to speak to him and reveal to him secrets.^[6]

Óðinn then appointed Njörðr and Freyr to be priests of sacrificial customs and they became Diar ("Gods") of the people of Asgard. Freyja, described as daughter of Njörðr, was the priestess of these sacrifices, and here she is described as introducing seiðr to Asgard.^[6]

A number of theories surround the Æsir–Vanir War:

As the Vanir are often considered fertility gods, the Æsir–Vanir War has been proposed as a reflection of the invasion of local fertility cults somewhere in regions inhabited by the Germanic peoples by a more aggressive, warlike cult.^[3] This has been proposed as an analogy of the invasion of the Indo-Europeans.^[3] Georges Dumézil stated that the war need not necessarily be understood in terms of historicity more than any other myth however.^[7]

Scholars have cited parallels between the Æsir–Vanir War, The Rape of the Sabine Women from Roman mythology, and the battle between Devas and Asuras from Hindu mythology, providing support for a Proto-Indo-European "war of the functions." Explaining these parallels, J. P. Mallory states:

Many scholars consider the figures of Gullveig/Heiðr and Freyja the same.^[9] These conclusions have been made through comparisons between the figure of Gullveig/Heiðr's use of seiðr in Völuspá and the mention of Freyja introducing seiðr to the Æsir from the Vanir in Heimskringla.^[3] This is at times taken further that their corruption of the Æsir led to the Æsir–Vanir War.^[3]

Lindow states that he feels that even if the two are not identical, the various accounts of the war seem to share the idea of a disruptive entry of persons into a people.^[3] Lindow compares the appearance of Gullveig/Heiðr into the Æsir to that of Hœnir and Mímir's disruption amongst the Vanir in Heimskringla.^[3] Lindow further states that all three accounts share the notion of acquisition of tools for the conquest of wisdom; the practice of seiðr in two accounts and the head of Mímir in one.^[3]