The modern Pentecostal movement has been studied many times in relation to its theological and sociological background. Previous studies, however, have not focused on the disctinctive doctrine of that movement: the teaching that speaking in tongues is the initial physical evidence of the Baptism in the Holy Spirit. Given that Pentecostals believe that this is a work of grace, such a doctrine seems unlikely to arise, as physical evidence is seldom required or looked for in the life of a believer in relation to any other area of grace. This prompts the question of why such evidence was even being looked for. And yet, within a very short time of its proposal, acceptance of this doctrine was so widespread as to become the hallmark of the movement. Insistence on such a doctrine led to many being asked to leave their denominations, and thus to the founding of other denominations. This book attempts to answer the question: "Why?" And specifically: "Why Tongues?" Kenneth R. Walters, Jr., Ph.D. 2010, Fuller Theological Seminary, is Adjunct Professor at Bethesda University of California in Anaheim, CA and the King's Seminary in Van Nuys, CA. He is Lead Pastor at West Valley Christian Center in Chatsworth, CA, and is married to Cheri Walters, also an ordained minister with the Assemblies of God. He has four children and two grandchildren.