The Pentecostal movement within protestant Christianity places emphasis on the supernatural sign gifts of the Holy Spirit, especially the gift of tongues first seen at Pentecost in Acts chapter 2. Pentecostalism is similar to the Charismatic movement, but developed earlier and separated from the mainstream church.
Theologically, most Pentecostal denominations are aligned with Evangelicalism in that they emphasize the Scriptures and the need for conversion to faith in Jesus. Most Pentecostals also adhere to the doctrine of Biblical inerrancy. Pentecostals differ from most Fundamentalists in their belief in the modern day operation and gifts of the Spirit.
Although "speaking in tongues" is often emphasized in Pentecostalism, the idea that one is not saved unless one speaks in tongues is rejected by most major Pentecostal denominations.
A small number of Pentecostal-type churches hold to Oneness theology, which decries the traditional doctrine of the Trinity as unbiblical. The largest Pentecostal Oneness denomination in the United States is the United Pentecostal Church. Oneness Pentecostals, are sometimes known as "Jesus-Name", "Apostolics", or by their detractors as "Jesus only" Pentecostals. This is due to the belief that the original Apostles baptized converts in the name of Jesus. The majority of Oneness Pentecostals believe that God has revealed Himself in different roles rather than three distinct persons, for which see modalism. Some modern Oneness adherents are in an effort to distance Oneness theology from ancient modalism because of the problems in the idea of God revealed in successive roles.
The major trinitarian pentecostal organizations, however, including the "Pentecostal World Conference" and the "Fellowship of Pentecostal and Charismatic Churches of North America", have condemned Oneness theology as a heresy and refuse membership to churches holding this belief. The same holds true for the Oneness Pentecostal towards trinitarian churches. It should be noted that the Apostolic Church (UK) is also a strongly Trinitarian Pentecostal denomination.