The Norns are the Goddesses of destiny. Three spirits who spin the thread of life for all living beings, gods, men, giants and dwarves. One spun out the thread of each life, another measured its length, and the third decided when the thread should be snapped. They control the destinies of both gods and men, as well as the unchanging laws of the cosmos. they were respected by all for the immense power they possessed over the destinies of gods and humans alike. Once the Norns had decided someone's fate, that destiny could not be changed. Even the principal god, Odin, was subject to their power. They are represented as three sisters: Urd ("fate"), Verdandi ("necessity") and Skuld ("being"). They live at the base of the World Tree Yggdrasil in the realm of Asgardnear Urd's Well.
Nothing lasts forever, and even the mighty Yggdrasil is subject to decay. The Norns try to stop this process, or at least slow it down, by pouring mud and water from the Well of Fate over its branches. This magical liquid stops the rotting process for the time being. These three Norns tended to the health of the World Tree, Yggdrasil. They kept it from withering. Every day they drew water from Urd's Well and sprinkled it over the tree, and they patched clay from the well onto the tree trunk in places where the bark had rotted away or been eaten by animals. Since Yggdrasil's roots and branches connected all the worlds and held the universe together, the Norns were thus responsible for preserving the fabric of all creation. The Norns have parallels in the three Fates (Parcae) of Greek and Roman mythology; thus they are believed to have originated prior to the development of the Oden legends and may be of Indo-European origin.
According to the 'Prose (or Younger) Edda', though Urd, Verdande, and Skuld were the principal Norns, there were many other Norns as well, some good and some evil, and whenever someone was born, a Norn would be there who would shape that person's life and determine his or her fate. Even the origins of Norns could be different; some were of divine origin, others originated with the elves and the dwarfs. Good Norns, ones of noble parentage, were believed to shape good lives, while evil Norns were responsible for misfortune.

Urd : is the oldest of the three sisters and is associated with the past or what was.
Verdandi : is associated with the present or what is.
Skuld : is associated with the future or what could be.