The modern Pentecostal movement traces its founding to a set of meetings that began in April 1906 at a former livery stable on Azusa Street in Los Angeles, led by William J. Seymour, an African American preacher who had studied under Charles Parham in Kansas. Seymour taught that speaking in tongues was the evidence that a believer had received the baptism in the Holy Spirit, a teaching Parham had already advanced, and the Azusa Street meetings ran nightly for roughly three years, drawing a racially mixed congregation that was itself remarkable in the segregated United States of the period, and reported by observers to include people speaking in tongues, falling to the floor and prophesying.
Visitors carried the practice home and planted it across denominations that became the Assemblies of God, the Church of God in Christ and dozens of smaller bodies, so that a single storefront revival is treated by historians as the direct root of a movement now counted in several hundred million adherents worldwide. The doctrine that tongues is the initial evidence of Spirit baptism became a dividing line almost immediately: classical Pentecostal bodies held to it as required, while the charismatic movement that spread through mainline Protestant and Catholic churches from the 1960s onward generally received the gift without adopting the evidential doctrine attached to it at Azusa Street. The distinction still separates Pentecostal denominations from the wider charismatic renewal that followed them by half a century.