Yggdrasil ("The terrible one's horse") is an ash tree that is located at the center of the universe. This tree is so vast that it's branches spread over heaven and earth alike. It is supported by three roots. The first is rooted in Asgard, the realm of the gods, it is rooted near the Urdar fountain, also known as Weird's Well. The second root is located in Jotunheim, the land of the frost-giants and is rooted near Mimir's well, whose waters contain wisdom and understanding. The third and final root reaches to the depths of Niflheim to drink from the stream Hvergelmir.

The topmost branch of this tree, is known as Lerad. An eagle is perched atop it, between whose eyes sits the falcon Vedfolnor who looks over all the worlds with his gaze, reporting all that he sees. At the foot of the tree, near Hvergelmir, lives the dragon Nidhogg who continuously gnaws at the roots of the great tree, along with many scores of lesser snakes, forever attempting to kill it, knowing that the death of the tree would signal the beginning of the downfall of the gods. The gods know that the death of this tree is a signal that the end is near. As a result the norns water it's roots each day with water from Mimir's Well to try and keep it in perfect health. Between the falcon Vedfolnor and Nidhogg, runs the squirrel Ratatosk whose duty it is to carry their taunts to each other.

Four deer run across the branches of the tree and eat the buds; they represent the four winds. There are other inhabitants of the tree, such as the squirrel Ratatosk ("swift teeth"), a notorious gossip, and Vidofnir ("tree snake"), the golden cock that perches on the topmost bough. The roots are gnawed upon by Nidhogg and other serpents. On the day of Ragnarok, the fire giant Surt will set the tree on fire.

The name Yggdrasil means the tree of universe, of time or of life.

Also known as: Yggdrasill, The World Tree, , The Ash Tree, The Yew Tree, The World Ash Tree, Ask Yggdrasil, Hoddmimir's Wood, Laerad, Odin's Horse

Old Norse: Mimameidr