Heinrich Glarean (c. 1488–1563) was a Swiss music theorist, composer, and music educator associated with the Renaissance period. He is best known for his influential work in music theory, particularly through his treatise "Dodecachordon" (1547), which introduced the concept of the "12 modes" and expanded the existing modal system from the traditional eight. This work significantly impacted the understanding of tonal organization and harmonic structures in Western music. Glarean's contributions also included compositions, although they are less well-documented than his theoretical writings. His music often reflected the polyphonic style of the time, characteristic of the early Renaissance. He was connected to notable figures in music, including the composer Heinrich Isaac, and his theories influenced later theorists and composers, including the likes of Giovanni Gabrieli and the Venetian school. His work laid the groundwork for the transition from modal to tonal music, thereby shaping the evolution of Western music theory and practice. Glarean's insights into music notation, harmony, and modal interchange continue to be studied and appreciated by musicologists and theorists today.