Lou Harrison’s compositions for Indonesian gamelan and Western instruments have served as representations of Harrison’s distinctive transcultural voice. His Concerto for Piano with Javanese Gamelan represents a fascinating musical synthesis between two great classical traditions. More than blending Eastern and Western instruments within a single composition, hidden beneath this juxtaposition lies a Harrison’s complex creative method. The purpose of this study is to examine Harrison’s method of forging Western and Javanese idioms within a single work. In order to gain a better understanding through musical analysis, I include chapters concerning the development of exoticism in twentieth-century Western music, with brief historical background on traditional Javanese gamelan, and Harrison’s compositional trajectory toward his Concerto for Piano with Javanese Gamelan. In this concerto, I provide critical understanding of his compositional process using both in Eastern and Western elements. The analysis covers both the macrocosmic and microcosmic structures of the musical form in each movement, pitch-class sets, and rhythmic complexity. Through this method, one can see how Lou Harrison synthesizes the piano successfully with the gamelan idiom by blending two distinct musical cultures, while also emphasizing and reconciling their idiosyncrasies.