"Traité de l'harmonie" is a foundational music theory text written by the French composer and theorist Jean-Philippe Rameau in 1722. The work explores the principles of harmony, emphasizing the importance of chords and their relationships. Rameau's ideas significantly influenced the understanding of tonal music and the structure of Western classical music. In this treatise, Rameau introduces concepts such as fundamental bass and chord progressions, which are essential for composers and musicians. His systematic approach laid the groundwork for future music theory, shaping the way harmony is taught and understood in both historical and contemporary contexts.