Mandaeism or Mandaeanism (Modern Mandaic: Mandaʻiūtā‎ (מנדעיותא); Arabic: مندائية‎ Mandāʼīyah/Mandāʾiyyah; Persian: مندائیان‎ Mandâ'iyân) is a gnostic religion^{[citation needed]} (Aramaic manda means "knowledge", as does Greek gnosis) with a strongly dualistic worldview.

Its adherents, the Mandaeans, revere Adam, Abel, Seth, Enosh, Noah, Shem, Aram and especially John the Baptist, but reject Jesus of Nazareth and are hostile to Christianity. They are sometimes identified with mentions in the Quran of the Sabian religion, particularly in an Arabian context, but the Sabian religious community is extinct today.

According to most scholars, Mandaeans migrated from the Southern Levant to Mesopotamia in the first centuries CE and are certainly of pre-Arab and pre-Islamic origin. They are Semites and speak a dialect of Eastern Aramaic known as Mandaic. They may well be related to the "Nabateans of Iraq" who were pagan, Aramaic speaking indigenous pre-Arab and pre-Islamic inhabitants of southern Iraq.