Up to now the teaching on baptism in the Holy Spirit has been based on a few scriptural texts, whose interpretation was disputed. This doubt cast its shadow on those who promote baptism in the Holy Spirit. Now new evidence has been found in early post-biblical authors (Tertullian, Hilary of Poitiers, Cyril of Jerusalem, John Chrysostom, Philoxenus, and the Syrians) which demonstrates that what is called baptism in the Holy Spirit was integral to Christian initiation (baptism, confirmation, Eucharist). Because it was part of initiation into the Church, it was not a matter of private piety, but of public worship. Therefore it was and remains normative. This is an intriguing ground-breaking study of value to RCIA teams, pastors, theology teachers and students, and Church offices.