The name is a problem before the tree is.
Yggdrasill parses most naturally as Yggr + drasill: Ygg's horse. Yggr, "the terrible one," is one of Odin's bynames, and drasill is a poetic word for a steed. A horse belonging to Odin — but the object it names is an ash tree.
The usual explanation is grim and probably right. Hávamál stanzas 138–141 have Odin describe hanging on a windy tree for nine full nights, wounded with a spear, given to himself, on a tree of which no one knows from what roots it grows; no bread and no horn were passed to him; he peered down, took up the runes screaming, and fell back. "Riding the gallows" is a standard Norse euphemism for being hanged, and a gallows is a hanged man's horse. If the reading holds, the world tree is named after the instrument of a self-sacrifice, and the tree Odin hung on is this one — though Hávamál never says so, and the connection is inference.
The three roots and the two lists
Ask how many worlds hang off Yggdrasil and the answer everyone gives is nine. Ask which nine and the sources go silent. No surviving text lists them. Every diagram of the nine worlds you will find — arranged on three levels, tidily labelled — is a modern reconstruction assembled by picking place-names out of different poems. The number nine is genuine and recurs throughout Norse material; the roster is not.
Even the roots do not agree.
- Grímnismál gives three roots: one over Hel, one over the frost-giants, one over mankind.
- Gylfaginning gives three roots to three wells: one among the Æsir at Urðarbrunnr, one among the frost-giants at Mímir's well, and one over Niflheimr at Hvergelmir, gnawed by Níðhöggr.
Snorri's version is the famous one. It is also the one that reads like an editor tidying, since it converts a poem's rough three-way division of the cosmos into a symmetrical arrangement with a named well per root.
The tree is being destroyed while it stands
Grímnismál stanza 35 says the ash suffers more hardship than men know: a hart bites it above, its trunk rots, and Níðhöggr tears it below. This is the single most distinctive idea in Norse cosmology and it is easy to miss under the imagery.
Four harts — Dáinn, Dvalinn, Duneyrr and Duraþrór — crop the highest shoots. An unnamed eagle sits in the branches with a hawk called Veðrfölnir between its eyes. The squirrel Ratatoskr runs the trunk carrying malice between the eagle and the serpent below. Innumerable serpents lie in the roots with Níðhöggr. Meanwhile the norns haul water and clay from the well every day to stop the limbs withering.
Decay is not the tree's ending. It is the tree's ordinary condition. The structure of the Norse universe is a thing under continuous attack that continuous work keeps upright, and even the destruction at Ragnarök does not fell it — Fjölsvinnsmál and the survival of Líf and Lífthrasir inside "Hoddmímis holt," which many read as the tree itself, both leave it standing through the fire.
Ash, or yew?
Every text calls it an ash, askr. But Fjölsvinnsmál calls a world-tree Mímameiðr and says its branches spread over every land, and Yggdrasils askr is described in Gylfaginning as evergreen — barr — which an ash is emphatically not.
The yew has therefore been proposed: evergreen, extremely long-lived, associated with graveyards across northern Europe, and the source of an Old Norse word barraskr, needle-ash. Adam of Bremen's account of Uppsala describes a huge evergreen tree of unknown species standing beside the temple, always green, winter and summer, with a well next to it where a living human sacrifice was made. That is a tree-and-well cult site, described by a hostile Christian writer around 1075, and it is the closest thing to independent evidence that the mythological picture reflected a practice.
The Saxon Irminsul, a great wooden pillar destroyed by Charlemagne in 772, is often invoked as a Continental cognate. It was a column, not a tree, and what it represented is not recorded.
Where the halls are
Whether Yggdrasil is the frame of the cosmos or an object within it is never settled. Grímnismál lists the gods' dwellings without hanging them on branches. Ásgarðr is reached by riding over Bifröst, which implies horizontal geography rather than climbing. The gods hold court at a well among the roots. Læraðr, the tree by Valhalla that the goat Heiðrún and the hart Eikþyrnir feed from, is usually assumed to be Yggdrasil under another name — assumed, not stated.
The tree is also called Mímameiðr, Hoddmímis holt, Læraðr and simply askr Yggdrasils, and it is entirely possible these were originally several trees.
The dew, and the bees
One detail rarely quoted deserves to be. Völuspá says the ash stands ever green over the well of Urðr, and Snorri adds that the dew which falls from its limbs onto the earth is what men call honeydew, and that bees feed on it. It is a small piece of practical natural history — honeydew is a real substance, the sugary residue left on foliage by sap-feeding insects, and northern European beekeepers knew perfectly well that bees gather it. A cosmology that explains where honey comes from is a cosmology being used, not merely recited.
The most exported symbol in Norse mythology
Yggdrasil now appears on jewellery, tattoos, album covers, corporate logos and the flag of no country at all. It is a genuinely ancient image doing a very modern job — a legible emblem of interconnection, ecology and rootedness that requires no knowledge of the mythology to read. God of War built its entire cosmology on it; Marvel uses it as a branching multiverse; the ecological readings are late twentieth-century and none the worse for that. See symbol traditions for how the design has travelled, and world trees compared for how it stands against the axis-of-the-world images in other traditions.
What generally gets lost in transmission is the rot. The modern Yggdrasil is a serene image of unity. The medieval one is under permanent attrition, with a dragon at the bottom, a squirrel spreading slander up the middle, and the only reason it is alive being that somebody watered it this morning. For where it sits in the whole tradition, see the Norse overview.
Is Yggdrasil the tree Odin hanged himself on?
Almost certainly, and no text says so. Hávamál describes a windy tree, nine nights, a spear-wound and roots no one knows; Yggdrasill means the terrible one's steed; a gallows is a rider's horse in skaldic idiom. Three separate pieces fit together perfectly and none of them touches. This is characteristic of the Eddic corpus: the poems assume a body of knowledge their audience already had, and address it in allusions rather than statements.
Why does the world tree have a squirrel in it?
Because the cosmology is populated rather than diagrammatic. The eagle at the crown and the serpent at the root are a widely-attested opposition; what Norse adds is a messenger who carries insults between them for no purpose the sources give. The effect is to make the tree an inhabited place with ongoing business, quarrels and jobs — closer to a farmstead than to a cosmic principle. Norse mythology consistently prefers domestic detail to abstraction, and the squirrel is the clearest single example.
Did people actually make offerings at trees?
The evidence is good. Adam of Bremen's Uppsala grove, with bodies of men, dogs and horses hanging in it, is the most-quoted account; place-names in -lundr (grove) and -vé (sanctuary) are widespread across Scandinavia; and Continental Germanic sources record the felling of sacred trees by missionaries — Boniface and the oak of Thor at Geismar around 723 being the best-known. Sacred groves are far better attested archaeologically and textually than temple buildings, which is worth remembering whenever a retelling puts the Norse gods indoors.