The Ascendancy of Theravada Buddhism is a comprehensive study of the advent of Buddhism in Southeast Asia, especially in Thailand during the first millennium CE. The author, Prapod Assavavirulhakarn, presents new ideas about the ancient cultural geography of South and Southeast Asia, bringing fresh insights to the perennial problem of Indianization -- the translation of ideas, ideals, and technologies from India to societies across the Bay of Bengal. Prapod examines existing theories and finds them wanting. His presentation of the early Buddhist period challenges established opinions and offers alternative views of the complexities and uncertainties that uniquely shaped Buddhism. His interpretations are grounded in primary sources, including Sanskrit, Pali, and Chinese inscriptions. The Ascendancy of Theravada Buddhism is a welcome advance in the study of the neglected field of early Thai Buddhism.