The usual form of baptism among the earliest Christians was for the candidate to be immersed, either totally (submerged completely under the water) or partially (standing or kneeling in water while water was poured on him or her). While John the Baptist's use of a deep river for his baptism suggests immersion, "The fact that he chose a permanent and deep river suggests that more than a token quantity of water was needed, and both the preposition 'in' (the Jordan) and the basic meaning of the verb 'baptize' probably indicate immersion. In v. 16, Matthew will speak of Jesus 'coming up out of the water'. Phillip and the Eunuch also went down and came up out of water (Acts 8:38-39). Baptism is likened unto a burial in Romans 6:3. "Dip" is translated from baptō (βάπτω). The traditional depiction in Christian art of John the Baptist pouring water over Jesus' head may therefore be based on later Christian practice." Pictorial and archaeological evidence of Christian baptism from the 3rd century onward indicates that a normal form was to have the candidate stand in water while water was poured over the upper body. Other common forms of baptism now in use include pouring water three times on the forehead, a method called affusion.
Martyrdom was identified early in Church history as "baptism by blood", enabling martyrs who had not been baptized by water to be saved. 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. As evidenced also in the common Christian practice of infant baptism, baptism was universally seen by Christians as in some sense necessary for salvation, until Huldrych Zwingli in the 16th century denied its necessity.
Quakers and The Salvation Army practice Baptism with the Holy Spirit instead of baptism with water. Among denominations that practice baptism by water, differences can be found in the manner and mode of baptizing and in the understanding of the significance of the rite. Most Christians baptize "in the name of the Father, and of the Son, and of the Holy Spirit" (following the Great Commission), but some baptize in Jesus' name only. Much more than half of all Christians baptize infants; many others hold that only believer's baptism is true baptism. Some insist on submersion or at least partial immersion of the person who is baptized, others consider that any form of washing by water, as long as the water flows on the head, is sufficient. The term "baptism" has also been used to refer to any ceremony, trial, or experience by which a person is initiated, purified, or given a name.
The English word baptism is derived indirectly through Latin from the neuter Greek concept noun baptisma (Greek βάπτισμα, "washing-ism"), which is a neologism in the New Testament derived from the masculine Greek noun baptismos (βαπτισμός), a term for ritual washing in Greek language texts of Hellenistic Judaism during the Second Temple period, such as the Septuagint. Both of these nouns are derived from the verb baptizō (βαπτίζω, "I wash" transitive verb), which is used in Jewish texts for ritual washing, and in the New Testament both for ritual washing and also for the apparently new rite of baptisma. The Greek verb baptō (βάπτω), "dip", from which the verb baptizo is derived, is in turn hypothetically traced to a reconstructed Indo-European root *gʷabh-, "dip". The Greek words are used in a great variety of meanings.
Baptism has similarities to Tvilah, a Jewish purification ritual of immersing in water, which is required for, among other things, conversion to Judaism, but which differs in being repeatable, while baptism is to be performed only once. (In fact, the Modern Hebrew term for "baptism" is "Christian Tvilah".) John the Baptist, who is considered a forerunner to Christianity, used baptism as the central sacrament of his messianic movement. The apostle Paul distinguished between the baptism of John, ("baptism of repentance") and baptism in the name of Jesus, and it is questionable whether Christian baptism was in some way linked with that of John. Christians consider Jesus to have instituted the sacrament of baptism, though whether Jesus intended to institute a continuing, organized church is a matter of dispute among scholars.