Yggdrasil grew from Ginnungagap, the cosmic void before creation. Other
names for the tree in the Northern Tradition are Laeradr, which may come from "Hleradr" meaning "giver of protection" and Mimameidr meaning "Mimir's Tree". Mimir was a wise giant, one of the world's first beings. Later the tree becomes associated with Odin. The name Yggdrasil means "Ygg's Horse", Ygg ("Terrible One") being an aspect of Odin. It is also called "Odin's Gallows Steed", this referring to Odin's shamanic ordeal which enabled him to discover the power of the Runes. This is describe in the poem Hivamil: "I know that I hung on the windy tree, the nights all nine .... I looked below. I took up the runes - screaming I fell back from there". Odin did not invent the Runes but he learned their secrets, some of which he taught to humanity. He may not have been the first to make this discovery as there is a reference in the myths to Freya teaching Odin Runelore.

The significance of the horse in the name Yggdrasil is interesting as the horse is the favorite shamanic animal for travel between the worlds. There are other creatures associated with the tree. Niddhogr ("the one striking full of hatred") is a dragon or worm who, with a group of snakes, gnaws at the roots, symbolizing chaos. A squirrel called Ratatosk scurries up and down the tree relaying insults between the dragon and the eagle at the top who creates the wind by flapping his wings. Between his brows stands a falcon; this may symbolise the union of male and female. Four harts and a stag graze on the leaves and from the stag's antlers water drips into a spring which feeds all the rivers of the world. The bark is eaten by a goat called Heidrun, whose udders produce an endless supply of mead. Bees are
fed from the dew that falls from the tree.

The damage caused by the animals is repaired by the Norns, three goddesses who give to each of us a destiny to fulfill or to fight against. The three represent the past, present and future. The Norns repair and care for the tree, watering its roots and putting clay on its trunk. Beneath the tree are three springs, Urd's Well (Urd is one of the Norns), Mimir's Well(where the eye that Odin sacrificed, in exchange for a draught of the sacred Mead of Knowledge from Heimdall's horn, is hidden) and Hvergelmir, the bubbling cauldron where Niddhogr lives.

Yggdrasil is commonly described as an ash tree. This is unlikely as, in the mythology, it is always referred to as an evergreen. A more likely candidate is the evergreen yew tree. Nigel Pennick suggests that an old name for the yew, needle ash, is the source of this confusion. There may also be a clue in the name Yggdrasil. Schroder interprets this as yew pillar (yggia from igwja = yew, and drasil from dher = support). To the Celts the yew was the tree of death and resurrection which ties in with the Hebrew Tree of Life and the general theme of these trees.