Immersion baptism is a method of baptism that is distinguished from baptism by affusion (pouring) and by aspersion (sprinkling), sometimes without specifying whether the immersion is total or partial, but very commonly with the indication that the person baptized is immersed in water completely. The term is also, though less commonly, applied exclusively to modes of baptism that involve only partial immersion.

Baptism is a Christian sacrament of initiation almost invariably with the use of water. It may be performed by sprinkling or pouring water on the head, or by immersing in water either partially or completely, traditionally three times, once for each person of the Trinity. The synoptic gospels recount that John the Baptist baptised Jesus. 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. Baptism is also called christening, although some reserve the word "christening" for the baptism of infants. In certain Christian denominations, such as the Catholic Churches, Eastern Orthodox Churches, Oriental Orthodox Churches, Assyrian Church of the East, and Lutheran Churches, baptism is the door to church membership, with candidates taking baptismal vows. It has also given its name to the Baptist churches and denominations.