Oneness Pentecostalism is a significant part of Pentecostal and Charismatic Christianity with a worldwide constituency of over thirty million. The distinctive teaching of Oneness theology is that there is one God with no distinction of persons in God’s eternal being and that Jesus Christ is the fullness of the one God incarnate. A related teaching is that initiation into the New Testament church consists of repentance, water baptism in the name of Jesus Christ, and the baptism of the Holy Spirit with the initial sign of tongues (Acts 2:37–39). The chapter begins with an exploration of the origins of modern Oneness Pentecostalism and then details Oneness theology based on the consensus of contemporary Oneness scholarship. It suggests that underlying Oneness theology is an Apostolic hermeneutic based on a thoroughgoing restorationism: Oneness Pentecostals view the first-century apostolic church as the model and seek to restore its teachings and practices.