Pentcostalism is a relatively new religious movement, having its beginnings, most authorities say, in 1901, with the teachings of Midwestern preacher Charles Fox Parham. He taught that speaking in tongues, or glossolalia, would be the movement that would empower the Christian church for the "last days harvest" by serving to evangelize the world. Six years later, an intense outbreak of tongue speaking in Los Angeles, when an African-American disciple of Parham, William J. Seymour, led his church in a much larger and more influential exercise of the practice, essentially initiated the expansion that has made Pentecostalism the fastest-growing Protestant denomination in the world. Today this movement is the largest religious division to have originated in the United States, with churches in 385 of the 399 counties of Appalachia.

In West Virginia and Appalachia there has been a fusing of Pentecostal theology and the Holiness movement, the latter being a development from the early Wesleyan faith. John Wesley, who along with his brother, Charles, founded the Methodist church, contended that simple conversion or initial redemption should not constitute the end-all of Christian development. Rather, the convert should continue throughout his or her spiritual life to climb toward perfection in sacred development, practicing a pietistic lifestyle that in its ultimate form would be called Sanctification.

In Appalachian Pentecostalism, this holiness state would become linked with the anointment of the Holy Spirit, a spiritual condition which was thought to permit the believer to engage in speaking in tongues, healing the sick, casting out demons, taking up serpents, and drinking deadly poisons (the five signs of a believer as pronounced in Mark 16:17—18). Consequently, in West Virginia and other areas of Central Appalachia we find many churches that are identified as Pentecostal Holiness or Holiness Pentecostal. Perhaps the most interesting division between Pentecostal churches in West Virginia and in most states of Central Appalachia is the theological split that separates the "Trinitarian Pentecostals," who baptize in the name of the Father, the Son, and the Holy Spirit, and the "Oneness Pentecostals," who baptize only in the name of Jesus. In some cases the Oneness Pentecostals formally reject the Trinity, but in other cases they proclaim that they are Trinitarians and that their baptism only in the name of Jesus simply celebrates the importance John the Baptist placed on the role of Jesus in the original River Jordan baptisms.

Of the 55 West Virginia counties there are only three that have no Pentecostal churches at all, as of a 2000 church census. However, it must be noted that some Pentecostal denominations do not have "Pentecostal" in their formal title. This is true for the Assemblies of God; the Church of God Cleveland, Tennessee; the Church of God of Prophecy; the Church of God, Mountain Assembly; the Fire Baptized Holiness Association; the International Church of the Foursquare Gospel; the Open Bible Standard Churches; and the Original Church of God. Of these, Assemblies of God, the Church of God Cleveland, Tennessee, and the Church of God of Prophecy have numerous fellowships in West Virginia.

It is difficult to document the size of the Pentecostal movement because so many of the churches are totally independent, belonging to no organization above the local fellowship and frequently keeping no formal membership records even of their own congregation. Such church polling organizations as the Glenmary Research Center of Nashville frequently must depend on computer-generated models that produce only estimates of regional, state, or national counts.