The Pentecostal movement is by far the largest and most important religious movement to originate in the United States. Beginning in 1901 with only a handful of students in a Bible School in Topeka, Kansas, the number of Pentecostals increased steadily throughout the world during the Twentieth Century until by 1993 they had become the largest family of Protestants in the world. With over 200,000,000 members designated as denominational Pentecostals, this group surpassed the Orthodox churches as the second largest denominational family of Christians, surpassed only by the Roman catholics. In addition to these "Classical denominational Pentecostals," there were over 200,000,000 "Charismatic" Pentecostals in the mainline denominations and independent charismatic churches, both Catholic and Protestant, which placed the number of both Pentecostals and charismatics at well over 420,000,000 persons in 1993. This explosive growth has forced the Christian world to pay increasing attention to the entire movement and to attempt to discover the root causes of this growth.

Although the Pentecostal movement had its beginnings in the United States, it owed much of its basic theology to earlier British perfectionist and charismatic movements. At least three of these, the Methodist/Holiness movement, the Catholic Apostolic movement of Edward Irving, and the British Keswick "Higher Life" movement prepared the way for what appeared to be a spontaneous outpouring of the Holy Spirit in America.

Perhaps the most important immediate precursor to Pentecostalism was the Holiness movement which issued from the heart of Methodism at the end of the Nineteenth Century. From John Wesley, the Pentecostals inherited the idea of a subsequent crisis experience variously called "entire sanctification,"" perfect love," "Christian perfection," or "heart purity." It was John Wesley who positioned such a possibility in his influential tract a plain Account of Christian Perfection (1766). It was from Wesley that the holiness movement developed the theology of a "second blessing." It was Wesley’s colleague, John Fletcher, however, who first called this second blessing a "baptism in the Holy Spirit," an experience which brought spiritual power to the recipient as well as inner cleansing. This was explained in his major work, Checks to Antinominianism (1771). During the nineteenth century, thousands of methodists claimed to receive this experience, although no one at the time saw any connection with this spirituality and speaking in tongues or any of the other charisms.

In the following century, Edward Irving and his friends in London suggested the possibility of a restoration of the charisms in the modern church. A popular Presbyterian pastor in London, Irving led the first attempt at "charismatic renewal" in his Regents Square Presbyterian Church in 1831. Although tongues and prophecies were experienced in his church, Irving was not successful in his quest for a restoration of New Testament Christianity. In the end, the “Catholic Apostolic Church” which was founded by his followers, attempted to restore the "five-fold ministries" (of apostles, prophets, evangelists, pastors, and teachers) in addition to the charisms. While his movement failed in England, Irving did succeed in pointing to glossolalia as the "standing sign" of the baptism in the Holy Spirit, a major facet in the future theology of the Pentecostals.

Another predecessor to pentecostalism was the Keswick "Higher Life" movement, which flourished in England after 1875. Led at first by American holiness teachers such as Hannah Whitall Smith and William E. Boardman, the Keswick teachers soon changed the goal and content of the "second blessing" from the Wesleyan emphasis on "heart purity" to that of an "enduement of spiritual power for service." Thus, by the time of the Pentecostal outbreak in America in 1901, there had been at least a century of movements emphasizing a second blessing called the "baptism in the Holy Spirit" with various interpretations concerning the content and results of the experience. In America, such Keswick teachers as A.B. Simpson and A.J. Gordon also added to the movement at large an emphasis on divine healing "as in the atonement" and the premillenial rapture of the church.