Adoptionism, also called dynamic monarchianism, is an early Christian nontrinitarian theological doctrine, subsequently revived in various forms, which holds that Jesus was adopted as the Son of God at his baptism, his resurrection, or his ascension. How common adoptionist views were among early Christians is debated, but it appears to have been most popular in the first, second, and third centuries. Some scholars see adoptionism as the belief of the earliest followers of Jesus, based on the epistles of Paul and other early literature. However, adoptionist views sharply declined in prominence in the fourth and fifth centuries, as Church leaders condemned it as a heresy.

Nontrinitarianism is a form of Christianity that rejects the mainstream Christian theology of the Trinity—the belief that God is three distinct hypostases or persons who are coeternal, coequal, and indivisibly united in one being, or essence. Certain religious groups that emerged during the Protestant Reformation have historically been known as antitrinitarian.