Ry ichi Ab presents the most thorough and innovative study to date on the Buddhist figure K kai (774 - 835) -- one that constitutes a radically different approach to the research on early Japanese religious history. K kai is generally credited with the formal establishment of tantric -- or esoteric -- Buddhism in Japan and as the founder of the Shingon school of Buddhism. Ab contends that the importance of K kai's transmission of esoteric Buddhism to Japan lay not in the foundation of a new sect but in his creation of a general theory of language grounded in the ritual speech of mantra.