The advocacy of adult baptism on the grounds that only as adults can people responsibly accept and declare their faith: Anabaptism is a term given for those who practice re-baptizing mature Christian converts who already have been baptized as infants.

The churches of western Christendom that separated from the Roman Catholic Church during the Reformation resulting in some Protestant movements in the 16th century that believed that the Bible was the most important guidance for Christians and so some of them were practitioners of Anabaptism because they were convinced that only those who were old enough to make decisions to become baptized believers, and not infants, were the true believers.