Pentecostalism is an expression of orthodox Christianity, which emphasizes the Holy Spirit in belief and practice. While the movement, and it's various denominations, is relatively new, Pentecostalism has become one of the largest and fastest-growing branches of the Christian religion. It's estimated that the movement has 500 million adherents worldwide. While the modern-expression of Pentecostal Christianity began in America in the early 20th century, by the beginning of the 21st century, the movement gained significant strength in Africa, Asia, and South America as well.
To understand the movement one must become familiar with its history and the individuals that comprise it. Like other expressions of Christianity, the movement has successes and failures, unification and division, protagonists and antagonists. Yet what has united all Pentecostals is the testimony of having experienced a unique gifting of the Holy Spirit similar to the one the church experienced on the day of Pentecost as recorded in the New Testament.