Biblical unitarianism (otherwise capitalized as biblical Unitarianism, sometimes abbreviated as BU) is a Unitarian Christian denomination whose adherents affirm the Bible as their sole authority, and from it base their beliefs that God the Father is one singular being, and that Jesus Christ is God's son but not divine. The term "biblical Unitarianism" is connected first with Robert Spears and Samuel Sharpe of the Christian Life magazine in the 1880s. It is a neologism (or retronym) that gained increasing currency in nontrinitarian literature during the 20th century as the Unitarian churches moved away from mainstream church traditions and, in some instances in the United States, towards merger with Universalism. It has been used since the late 19th century by conservative Christian Unitarians, and sometimes by historians, to refer to scripture-fundamentalist Unitarians of the 16th–18th centuries.

A few denominations use this term to describe themselves, clarifying the distinction between them and those churches which, from the late 19th century, evolved into modern British Unitarianism and, primarily in the United States, Unitarian Universalism.

The history of Unitarianism was as a "scripturally oriented movement" which denied the Trinity and held various understandings of Jesus. Over time, however—specifically, in the mid-19th century—some proponents of Unitarianism moved away from a belief in the necessity of the Bible as the source of religious truth. The nomenclature "biblical" in "biblical Unitarianism" is to identify the groups which did not make such a move.