Mark White & Charles H. Kraft 
Behind Enemy Lines [PDF ebook] 

Charles H. Kraft is Professor Emeritus at Fuller Seminary after forty-one years as Professor of Intercultural Communication. He has taught anthropology, communication, contextualization, and spiritual warfare to missionaries and prospective missionaries, in addition to serving as a missionary in Nigeria. He holds degrees from Wheaton College (BA), Ashland Theological Seminary (BD), and Hartford Seminary Foundation (Ph D) and is the author of thirty-two books and numerous articles in his fields of expertise.