Valentinianism was one of the major Gnostic Christian movements. Founded by Valentinus in the 2nd century AD, its influence spread widely, not just within Rome but also from Northwest Africa to Egypt through to Asia Minor and Syria in the East. Later in the movement's history it broke into an Eastern and a Western school. Disciples of Valentinus continued to be active into the 4th century AD, after the Roman Emperor Theodosius I issued the Edict of Thessalonica (380 AD), which declared Nicene Christianity as the State church of the Roman Empire.

The doctrine, practices and beliefs of Valentinus and the Gnostic movement that bore his name were condemned as heretical by proto-orthodox Christian leaders and scholars. Prominent Church Fathers such as Irenaeus of Lyons and Hippolytus of Rome wrote against Gnosticism. Because early church leaders encouraged the destruction of Gnostic texts, most evidence for the Valentinian theory comes from its critics and detractors, most notably Irenaeus, since he was especially concerned with refuting Valentinianism.