King Sejong wrote the verses in vernacular and compiled this book in the twenty-ninth year of his reign (1447), after he read the A Biography of the Buddha (Seokbo Sangjeol 釋譜詳節) written by his second son Prince Suyang (later King Sejo). The Moon’s Reflection on a Thousand Rivers is a long epic poem celebrating the life of Sakyamuni Buddha. According to the Buddha’s Biography and Its Eulogy (Worin Seokbo 月印釋譜), which includes both The Moon’s Reflection on a Thousand Rivers and A Biography of the Buddha, it contained a total of 583 short episodes (chang) in verse, 194 of which are contained in the first volume. Among its main features, it must be pointed out that characters in Hangul are bigger in size, whereas hanja are smaller and realized in the Gabin font of 1434. The Song of the Moon’s Reflection on a Thousand Rivers is even more valuable because it starts immediately in vernacular and not, as the most texts, in hanmun, and it contains a significant amount of terms of pure Korean origin.