Underlying principles on the origin and establishment of the concept fo Right-and-Left (R-&-L) in Korean traditional costume is studied in this paper. Among Korean traditional costumes, ordinary and funeral costumes are considered in this study. Thed concept of R-&-L expanded into different elements of daily life among Korean people is also considered as a process of conceptual development : starting from astron-omy principle, then developed to pragmatism principle, and expanded to abstraction principle. No evidence on the case where the astro-omy principle was directly applied to was found in this study. In most cases, pragmatism and abstraction principles are observed as underly-ing principles. In ordinary costumes, pragmatism principle is the fundamental base for R-&-L through right-hand-use rule. Even though abstraction prin-ciple was found in some ordinary costumes, we believe that this was generated for adding more meanings in addition to the pragmatism principle. In funeral costumes, pragmatism principle was almost totally ignored unlike in ordinary costumes because the funeral rite was performed though formality with abstract thoughts. The abstraction principle was exercised with the form of simple-discrimination rule based on the dual system along with Yin-Yang related cultural rules such as‘Yang-left-and-Yin-right’or‘father-left-and-mother-right’. However, the case where‘left-male-and-right-female’rule is applied to was not found in this study.