Pentecostalism began on the American frontier, and it has become one of the largest expressions of global Christianity. In less than a century, it has grown to hundreds of millions of adherents. Today, Pentecostalism is pan-denominational. There are charismatic Catholics and Lutherans, unaffiliated Pentecostal communities, and established Pentecostal traditions, most prominently the Assemblies of God. Host Krista Tippett speaks with a theologian about the rise of Pentecostal worship among African-Americans in every denomination and a sociologist on her study of modern day Pentecostals — whom she sees as mystics among us.