An eternal green ash tree in Norse Mythology, it stands in the middle of the world and it's branches spread out over all of the 9 realms, each realm had it's own branch, but if the tree itself were to shake, or fall; so will the realms.

Also known as "Mirmir's tree"( or Mimamelor) and "Laerad"( or Laleror). The idea of a world tree is also among other Germanic Tribes, in Saxoney, Germany, pagan's worshipped a tree known as "Trminsul", this tree eventually was destroyed by "Charlemagne" during the Saxton war in the 8th century.

The name Yggdrasil is a kenning, mythologica metaphor described in the Edda poem"Havamal". Yggdrasil is made of two words: Yggr ( one of odin's names, meaning terrifier), Drasill ( meaning majestic horse), therefore, the name Yggdrasil means "odin's horse".

The name is understood in the context of odin's connection to the world tree, odin once sacrificed himself on the tree to gain more knowledge. When he was hanging on the tree, he was therefore, riding the tree like a horse ( metaphor can seen as humerous), making this seen as norse humour.

"No one gave me bread nor a horn,

I looked down,

I took the runes, screaming I took,

I fell from the there.

    ----Havamalstanza 39

In the final minutes, before odin fell from Yggdrasil, was when he learned the secrets of the runes. We see everyday that knowledge is not gained without some persoal sacrifice in return( in norse mythology).

Yggdrasil was carried by huge roots, all with a "Well" next to them. The first root is deep belown the thick ice of Niflheim, in fact, so deep under the ground that it takes odin's' horse ( nine days at full speed through the dark valley's to make it to the root.

Where the realm of  Helheim is located, not much is known about the well here, and it could have some undiscovered benefit's that only the shadow's of the realm know.

The well is sometimes referenced to as the "well of poison", but it is also the source of life, it is from this well that the liquid came, which created the first being in mythology.

The root in the depths of  Helheim is struggling everyday to maintain it's strength because the great dragon "Niohoggr"( meaning hateful striker) is constantly chewing on it , he only stop's when he hears the "hellhound" Garmr howling in the distance.

At this moment, Niohoggr will spread it's wing's and fly to the entrance of Hel, where new dead souls have arrived. He will fly down and land next to them, taking all the blood out of the corpses, making them all turn pale.

According to the lay of Grimnir, niohoggr is not alone at the root, countless snakes are biting at the tree shoots. 

"More snakes
lie under the ash yggdrasil
than any old fool imagines,
Going and Moin,
they are Gragvitnir's sons,
Garabak and Grafvollud, and Ofhir and Svafnir
will always, i believe
eat away the tree shoots.
         ----grisnismal 34

When niohggr is chewing on the roof, he is often interupted by Ratatoskr ( meaning "Drill Tooth") who fills his ears with insults, ratatoskr is a annoyingg squirrel who runs up and down the tree from the dragon, to the eagle at the top.

When the eagle insult's niohggr, the squirrel runs down the tree, to tell the dragon what was said about him. The squirrel then runs back up the tree to the eagle, and tells him what the dragon said about him. His involvement as a messenger , keeps hatred between the dragon and the eagle alive.

Not much is known about the eagle, it's described in the "Prose Edda", to possess the knowledge of many things. It must be bigger than any eagle, because it has a hawk known as "Vedrfolnir" between it's two eyes.

The hawk is associated with the knowledge of the eagle, just like odin's two raven's, fly out to gather knowledge. Although it is said that there are both the hawk, and the eagle at the top of the tree. ( so part is uncertain)

The second root is in Jotunheim, this root is a well known as "mirmir's well", this is the well of wisdom, and belongs to Mimir. Every mimir drinks from the well using his drinking horn known as "Gajallarhorn"( this horn has the same name as the horn used by heimdallr, so it's possible that they have one each.)

Mimir allows other's to drink from the well to , but at a heavy price, odin once drank from the well of wisdom, but he had to sacrifice his right eye as his payment.

Mimir's well is the only great thing in Jotunheim, the rest is just a grim place, nothiing grows there except trees, and grass. But the river's are filled with "fresh" water, and seeps down to nourish the roots of all of the trees. 

The third root is in Asgard, next to the well known as Uror, next to this well is a hall, where 3 female beings known as Norns live, they are percived as the personification of time, their names are: Uror, Skuld, and Veroandi.

Every morning, these norns drew water from the well, and collect the moist earth, or clay around it, then pour it over the tree yggdrasil, ,this is done to keep the world tree green, and healthy. If they fail this task, the tree will start to rot.

The water from Uroarbrunnor is magical, so sacred that everything it touches (besides yggdrasil) becomes as white as the membrane (skin) inside of on eggshell. It is from this well the swans originate ( norse mythology), the white colour is a symbol of cleanliness, pride, beauty, greatness, light, and death.

It is also here that the god's and godesses have daily meetings, there tget cast judgment. This place is known as "Tinget", and during the viking age( this is compared to a parliment), for example, in Denmark the parliment is known as "Folketinget", the peoples parliment.

At ragnarok, the two last humans Liv and Livtraser, will find shelter inside yggdrasil, they will stay here until the world is safe to return to. They will become the ancestors of future humans.

According to a german medievil historian, there was a great tree in Uppsala, Sweden, that had branches that always stretched around it, always green( even in winter), and the type is unknown, but it's possible it was a pine tree. According to him, pagan's who lived there sacrificed to the god's at a near-by lake.

There are other creatures among the branches of  yggdrasil as well, on the roof of  Valhalla, stands the "Goat (Heidrun) and the "Stag"(Eikthyrnir). The stag spends it's days eating the new cutting-down's from the tree, while the goat eat's the leaves.

The goat udders endless streams of "mead"into a big tub in valhalla, every evening after the warriors have practised for Ragnarokk, they sit down in this hall to relax, eat the meat from  giant pig, (Saehrimnir) and drink the mead from the goat.

Among the green branches, live 4 other stag's known as Dainn, Duneyrr, and Duropror. they are busy spending their day devouring the leaves from the tree