This essay aims to understand the impact of the East Asian diffusion of The Complete Works of Naturality and Truth (Xing Li Da Quan 性理大全, Naturality and Truth hereafter). To this end, the essay discusses the processes of the adoption of Naturality and Truth in Chosun and Vienam and compares how the two versions of Essentials of The Complete Works of Naturality and Truth (Xing Li Da Qu an Je Yao 性理大全節要, Essentials hereafter) were formed in the differing contexts of the two kingdoms. Naturality and Truth, together with The Complete Works of the Five Classics and The Complete Works of the Four Books, were revised by a team of scholars led by Hu Guang under the commission of Emperor Yongle in 1415. Four years later, the emperor further ordered these three works be given to Chosun and Vietnam, which subsequently became the foundation upon which Neo- Confucianism took shape in these two kingdoms. Nevertheless, only Naturality and Truth had Essentials in both kingdoms. Confucian scholars in both states were responsible for producing their own versions of Essentials, and Kim Chung-Kook (1485-1541), a member of Jo Gwangjo faction, and Bùi Huy Bích (1744-1818), a student of prominent scholar Lê Quý Đôn, were in charge of the editorial tasks in Cho sun and Vietnam, respectively. Kim Chung-Kook and Bùi Huy Bích abridged Naturality and Truth in accordance to the needs of their own kingdoms, and their selective appropriations provide important materials for examining the Neo-Confucian thoughts in the two states, demonstrating the transformation of classical works in differing foreign contexts.