Baptism (from the Greek noun βάπτισμα báptisma) is a Christian rite of admission and adoption,[1] almost invariably with the use of water, into Christianity.[2][3] It may be performed by sprinkling or pouring water on the head, or by immersing in water either partially or completely, traditionally three times for each person of the Trinity.[4][5][6] The synoptic gospels recount that John the Baptist baptised Jesus.[7][8][9][10] Baptism is considered a sacrament in most churches, and as an ordinance in others. Baptism according to the Trinitarian formula, which is done in most mainstream Christian denominations, is seen as being a basis for Christian ecumenism, the concept of unity amongst Christians.[11][12] Baptism is also called christening,[13][14] although some reserve the word "christening" for the baptism of infants.[15] In certain Christian denominations, baptism is the door to church membership.[16] It has also given its name to the Baptist churches and denominations.

Masaccio (1425–1426). Baptism of the Neophytes [it]. Brancacci Chapel, Florence. This painting depicts baptism by affusion. The artist may have chosen an archaic form for this depiction of baptism by St. Peter.

Martyrdom was identified early in Church history as "baptism by blood",[17] enabling the salvation of martyrs who had not been baptized by water. Later, the Catholic Church identified a baptism of desire, by which those preparing for baptism who die before actually receiving the sacrament are considered saved.[18] Some Christian thinking regards baptism as necessary for salvation, but some writers, such as Huldrych Zwingli (1484–1531), have denied its necessity.[19]

Quakers and the Salvation Army do not practice water baptism at all.[20] Among denominations that practice water baptism, differences occur in the manner and mode of baptizing and in the understanding of the significance of the rite. Most Christians baptize using the trinitarian formula "in the name of the Father, and of the Son, and of the Holy Spirit"[21] (following the Great Commission), but some baptize using Jesus' name only. Much more than half of all Christians baptize infants;[lower-alpha 1] many others regard only adult baptism as true baptism.[citation needed]

The term "baptism" has also been used metaphorically to refer to any ceremony, trial, or experience by which a person is initiated, purified, or given a name.[22]