In the 14th century, the heir apparent to the throne of the central Thai kingdom completed the first truly literary work of a Thai author. Phya Lithai entitled his work Sermon on the Three Worlds but it later became known as Three Worlds of King Ruang. It is the culmination of a long history of visionary and cosmological literature within the Theravada tradition, representing in a vivid and concise form, the religious universe within which Thai Buddhists have traditionally lived. In particular, the description of death and the fates which await beings who die in the thirty-one realms of the Three Worlds portray the process of dying and depict the relative absence of suffering and pollution at high levels of attainment.Because of the prestige of its author, its claim to orthodox authority and its strong popular appeal, this text exerted a powerful influence on the religious consciousness of the Thai, on their literary and artistic development and on their social and ethical attitudes. Despite harsh criticisms to which the texts have been subjected by a number of Buddhist modernists in the nineteenth and twentieth centuries, this influence has persisted to the present day. Thus, not only from a buddhological point of view, but also from a historical or anthropological perspective, it is no exaggeration to say that the Three Worlds of King Ruang is the most important and fascinating text that has been composed in the Thai language.