In Christianity, baptism (from Greek baptizo: "immersing", "performing ablutions") is the ritual act, with the use of water, by which one is admitted to membership of the Christian Church and, in the view of some, as a member of the particular Church in which the baptism is administered.

The usual form of baptism among the earliest Christians was for the candidate (or "baptizand") to be immersed totally or partially. While John the Baptist's use of a deep river for his baptism suggests immersion, pictorial and archaeological evidence of Christian baptism from the 3rd century onwards indicates that the 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.