Manichaeism ( /ˈmænɨkiːɪzəm/; in Modern Persian آیین مانی Āyin e Māni; Chinese: 摩尼教; pinyin: Móní Jiào) was a major gnostic religion, originating in Sassanid era Babylonia. Although most of the original writings of the founding prophet Mani (in Persian: مانی, Syriac: ܡܐܢܝ, Latin: Manichaeus or Manes) (c. AD 216–276) have been lost, numerous translations and fragmentary texts have survived.

Manichaean as used in contemporary popular discourse refers to someone who sees the world as a struggle between Good and Evil (see Figurative Use, below).

Manichaeism taught an elaborate cosmology describing the struggle between a good, spiritual world of light, and an evil, material world of darkness. Through an ongoing process which takes place in human history, light is gradually removed from the world of matter and returned to the world of light from which it came. Its beliefs were based on local Mesopotamian gnostic and religious movements,

Manichaeism as a syncretistic form of oriental Christianity was quickly successful and spread far through the Aramaic-Syriac speaking regions, it thrived between the third and seventh centuries, and at its height was one of the most widespread religions in the world. Manichaean churches and scriptures existed as far east as China and as far west as the Roman Empire. It was widespread among the legions of the Roman Empire, who considered it a soldier's religion, and it was briefly the main rival to Christianity in the competition to replace classical paganism. Manichaeism survived longer in the East than in the West, and it appears to have finally faded away after the 14th century in southern China, contemporary to the decline in China of the Church of the East – see Ming Dynasty.

An adherent of Manichaeism is called, especially in older sources a Manichee. The religion is also referred to as Manicheanism (or Manichaeanism) and its adherents as Manicheans (or Manichaeans). By extension, the term "manichean" is widely applied (often disparagingly) as an adjective to a philosophy or attitude of moral dualism, according to which a moral course of action involves a clear (or simplistic) choice between good and evil, or as a noun to people who hold such a view.

Read more about Manichaeism:  Primary Sources, Figurative Use