In ancient Greek religion and mythology, the Moirai (/ˈmɔɪraɪ, -riː/)—often known in English as the Fates—were the personifications of destiny. They were three sisters: Clotho (the spinner), Lachesis (the allotter), and Atropos (the inevitable, a metaphor for death). Their Roman equivalent is the Parcae.

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.

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.

The word Moirai, also spelled Moirae or Mœræ, comes from Ancient Greek: μοῖρα, which means "lots, destinies, apportioners". It also means a portion or lot of the whole. It is related to meros, "part, lot" and moros, "fate, doom". The possible derived Latin meritum, "reward", English merit, maybe coming from the Proto-Indo-European language root *(s)mer, "to allot, assign".

In addition, Moira may mean

The three Moirai are known in English as the Fates. This derives from Roman mythology, in which they are the Parcae or Fata, plural of Latin: fatum, meaning prophetic declaration, oracle, or destiny; euphemistically, the "sparing ones". There are other equivalents that descend from the Proto-Indo-European culture.

In Norse mythology the Norns are a trio of female beings who rule the destiny of gods and men, twining the thread of life. They set up the laws and decided on the lives of the children of men.

Their names were Urðr, related with Old English wyrd, modern weird ("fate, destiny, luck"), Verðandi, and Skuld, and it has often been concluded that they ruled over the past, present and future respectively, based on the sequence and partly the etymology of the names, of which the first two (literally 'Fate' and 'Becoming') are derived from the past and present stems of the verb verða, "to be", respectively, and the name of the third one means "debt" or "guilt", originally "that which must happen". In younger legendary sagas, the Norns appear to have been synonymous with witches (völvas), and they arrive at the birth of the hero to shape his destiny.