Book excerpt: Composed while its author was the ruler of Tibet, Mirror of Beryl is a detailed account of the origins and history of medicine in Tibet through the end of the seventeenth century. Its author, Desi Sangye Gyatso (1653 - 1705), was the heart disciple and political successor of the Great Fifth Dalai Lama and the author of several highly regarded works on Tibetan medicine, including his Blue Beryl, a commentary on the foundational text of Tibetan medicine, The Four Tantras. In the present historical introduction, Sangye Gyatso traces the sources of influence on Tibetan medicine to classical India, China, Central Asia, and beyond, providing life stories, extensive references to earlier Tibetan works on medicine, and fascinating details about the Tibetan approach to healing. He also provides a commentary on the pratimoksha, bodhisattva, and tantric Buddhist vows. Desi Sangye Gyatso's Mirror of Beryl remains today an essential resource for students of medical science in Tibet.