The anniversary is being marked by denominational gatherings, the upcoming Pentecostal World Conference and a new 400-page book chronicling the movement now estimated to include more than 500 million worldwide.
"Beginning with only a handful of people in 1901, the number of Pentecostals increased steadily to become the largest family of Protestants in the world by the beginning of the 21st century," writes the Rev. Vinson Synan, author of "The Century of the Holy Spirit: 100 Years of Pentecostal and Charismatic Renewal."
But as their movement has grown, Pentecostals have become harder to identify. They retain their long-standing commitment to evangelism and vibrant worship services, but speaking in unknown tongues -- one of the most dramatic and signature elements of their worship -- is heard less frequently.
"The Pentecostals are getting more mainline and some of them are trying to be respectable," Synan said in a recent interview. "And then a lot of people come in who love the worship and never speak with tongues and they join the churches. You have maybe half or less of Pentecostals speak the tongues. The rest of them believe in it, but they just don't speak it."
Sherry DuPree, the immediate past president of the Society for Pentecostal Studies, said she is personally saddened by the trend. Now, more churches are known by the physical signs posted outside their buildings that declare their ties to Pentecostalism rather than the spiritual signs that used to emanate inside the church doors.
"The sign of the Spirit in some of them is gone," said DuPree, a member of the Church of God in Christ. "I hate to say so."
The Rev. Thomas Trask, general superintendent of the Assemblies of God and chairman of the Pentecostal World Conference, said one of the emphases of the gathering May 29-31 in Los Angeles will be on recapturing the focus on the Holy Spirit that long has been prized by Pentecostal Christians.
"There's still the work of the Spirit that makes it happen," he said. "It isn't organization. It isn't plans. It's God that has to do it."
He referred to a favorite Scripture from the Old Testament book of Zechariah: "`Not by might, nor by power but by my spirit, saith the Lord of hosts."'
Thousands of leaders of Pentecostal and charismatic churches from about 80 nations are expected to attend the triennial conference, which meets in this country for the second time since it began in 1947.
The vast array of representatives is part of a movement that began early in 1901 in Topeka, Kan., when a woman was baptized in the Holy Spirit and began speaking in tongues at a small Bible college. The movement gained global fame five years later, with the Azusa Street revival in Los Angeles.
Although the Los Angeles revival was unusual for its inclusion of people of both races, the Pentecostal movement has struggled with race relations since that time, with many denominations forming along racial lines. In 1994, during the so-called "Memphis Miracle" black and white Pentecostal leaders came together for reconciliation and formed the interracial Pentecostal/Charismatic Churches of North America.
Synan, a former general secretary of the Pentecostal Holiness Church, said some of the largest Pentecostal churches in the country are integrated but overall racial reconciliation in the movement remains "a huge challenge."
There also is a theological divide between Trinitarian Pentecostals and Oneness Pentecostals. The latter, who comprise about 10 percent of Pentecostals in the country but are not recognized by some Trinitarians, believe that Jesus was the only person in the Godhead and baptize in "Jesus' name" rather than "in the name of the Father, Son and Holy Ghost."
The movement has been known for its growth among diverse denominations and ethnic groups and its advancement of women. The Assemblies of God, the world's largest Pentecostal denomination, has a total of 15,000 ordained ministers in the United States and 4,000 -- or 27 percent -- are women.
"We just believe that that is right and there's a place for women in ministry within this church," said Trask, whose denomination held its first Women in Ministry conference in March.
In the 1960s, the movement among established Pentecostal denominations spread to mainline Protestant churches and to Catholic congregations, where its adherents are called charismatics.
In addition to tongues, some charismatic and Pentecostal worshippers experience other spiritual gifts, such as prophecy or healing. While some Christians believe such manifestations of the Holy Spirit ended in biblical times, Pentecostals and charismatics view them as modern-day phenomena that continue to aid in evangelism.
"Tongues was seen as a sign of the imminent second coming of Christ," explained Synan, dean of the School of Divinity at Regent University in Virginia Beach, Va. "Pentecostals felt a tremendous urgency to go out and convert the world before the second coming."
Nowadays, the missionary work, at first just aimed at Christian conversion, has evolved into church-building efforts. One of the largest churches is an Assemblies of God congregation in Seoul, South Korea, which claims to have 730,000 members.
Synan said although Pentecostals seek converts to Christianity and not Pentecostalism in particular, they believe the gifts of the spirit can influence potential converts.
"They feel that the gifts of the Spirit help you evangelize," he said. "When people are healed miraculously that draws people to the Lord."
Some of the most well-known faith healers, Benny Hinn and Reinhard Bonnke, draw huge crowds to their crusades in the United States and abroad.
Brother Jeffrey Gros, associate director of ecumenical and interreligious affairs for the National Conference of Catholic Bishops, has worked with Pentecostals and charismatics on both scholarly and grass-roots levels. He has watched non-Pentecostals advance from snickering at so-called "holy rollers" -- for their unusual worship style -- to realizing the charismatic version of Christianity is as authentic as others.
"There is a way in which the differences are so great and yet thereis a kind of sympathy that has developed where people have gotten to know each other," he said. As the movement has grown, it has influenced other churches and made inroads into secular culture. Music written by Pentecostals -- such as Jack Hayford's "Majesty" -- and expressive worship, such as the lifting of hands heavenward, has spread to churches without charismatic or Pentecostal leanings. Best-selling author and Pentecostal preacher T.D. Jakes of Dallas recently partnered with Hallmark Cards for a new "Loose Your Spirit" line in the Mahogany brand of African-American greeting cards. Pentecostals also have reached high political ranks in Latin America and in the United States, including Attorney General John Ashcroft.
"Because of their numbers and the vigor of the movement, you'll see politicians rising up like Ashcroft and still there were a lot of questions and prejudices against him because of his faith," Synan said.
Even as it has had success in both the spiritual and secular sectors, the movement also has had its share of scandals, most notably the sex and money troubles of televangelists Jim Bakker and Jimmy Swaggart in the 1980s.
"There were spectacular failures but despite that the heart of the movement continued to grow," said Synan said. "The big challenge after one whole century is to keep the fires burning into the next century."