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.

John the Baptist (Hebrew: יוחנן המטביל, Yoḥanan ha-mmaṭbil, Arabic: يحيى بن زكريا‎ Yahya ibn Zakariya, Aramaic: ܝܘܚܢܢ Yoḥanan, Greek: Ὁ Ἅγιος/Τίμιος Ἐνδοξος Προφήτης, Πρόδρομος καὶ Βαπτιστής Ἰωάννης Ho Hágios/Tímios Endoxos, Profḗtēs, Pródromos, kaì Baptistḗs Ioánnes) (c. 6 BC – c. AD 30-36) was an itinerant preacher and a major religious figure mentioned in the Canonical gospels and the Qur'an. He is described in the Gospel of Luke as a relative of Jesus who led a movement of baptism at the Jordan River. Some scholars maintain that he was influenced by the Essenes, who were semi-ascetic, expected an apocalypse, and practiced rituals corresponding strongly with baptism, although there is no direct evidence to substantiate this. John is regarded as a prophet in Christianity, Islam, the Bahá'í Faith, and Mandaeism.

Most biblical scholars agree that John baptized Jesus at "Bethany beyond the Jordan," by wading into the water with Jesus from the eastern bank. John the Baptist is also mentioned by Jewish historian Josephus, in Aramaic Matthew, in Pseudo-Clementine, and in the Qur'an. Accounts of John in the New Testament appear compatible with the account in Josephus. There are no other historical accounts of John the Baptist from around the period of his lifetime.