In ancient Greek religion and mythology, the Moirai, also spelled Moirae or Mœræ, are often known in English as the Fates. They were the incarnations of destiny. It was believed that the Fates would appear within three days of someone's birth to decide their fate. The three Moirai, or Fates, represented the cycle of life, essentially standing for birth, life, and death. They would spin (Clotho), draw out (Lachesis), and cut (Atropos) the thread of life.

The role of the Moirai was to ensure that every being, mortal and divine, lived out their destiny as it was assigned to them by the laws of the universe. For mortals, this destiny spanned their entire lives and was represented as a thread spun from a spindle. Generally, they were considered to be above even the gods in their role as enforcers of fate, although in some representations Zeus, the chief of the gods, is able to command them.

Their number became fixed at three: Clotho, "the spinner", Lachesis, "the allotter", and Atropos, “the unturnable", a metaphor for death.

The concept of a universal principle of natural order and balance has been compared to similar concepts in other cultures such as the Vedic Ṛta, the Avestan Asha (Arta), and the Egyptian Maat.