In Christianity, Sabellianism, (also known as modalism, modalistic monarchianism, or modal monarchism) is the nontrinitarian belief that the Heavenly Father, Resurrected Son and Holy Spirit are different modes or aspects of one God, as perceived by the believer, rather than three distinct persons in God Himself.The term Sabellianism comes from Sabellius, a theologian and priest from the third century.

Modalism differs from Unitarianism by accepting the Christian doctrine that Jesus was fully God.