In Norse mythology, Yggdrasil (/ˈɪɡdrəsɪl/ or /ˈɪɡdrəzɪl/; from Old Norse Yggdrasill, pronounced [ˈyɡːˌdrasilː]) is an immense tree that is central in Norse cosmology, in connection to which the nine worlds exist.
Yggdrasil is attested in the Poetic Edda, compiled in the 13th century from earlier traditional sources, and the Prose Edda, written in the 13th century by Snorri Sturluson. In both sources, Yggdrasil is an immense ash tree that is central and considered very holy. The gods go to Yggdrasil daily to assemble at their things. The branches of Yggdrasil extend far into the heavens, and the tree is supported by three roots that extend far away into other locations; one to the well Urðarbrunnr in the heavens, one to the spring Hvergelmir, and another to the well Mímisbrunnr. Creatures live within Yggdrasil, including the wyrm (dragon) Níðhöggr, an unnamed eagle, and the stags Dáinn, Dvalinn, Duneyrr and Duraþrór.
Conflicting scholarly theories have been proposed about the etymology of the name Yggdrasill, the possibility that the tree is of another species than ash, the relation to tree lore and to Eurasian shamanic lore, the possible relation to the trees Mímameiðr and Læraðr, Hoddmímis holt, the sacred tree at Uppsala, and the fate of Yggdrasil during the events of Ragnarök.