Harmonic structures refer to the way chords and notes are organized in music to create a sense of progression and resolution. They form the backbone of a musical piece, influencing its emotional impact and overall sound. Common harmonic structures include major and minor scales, which serve as the foundation for many compositions. In Western music, harmonic structures often follow specific patterns, such as the I-IV-V-I progression, where chords are built on the first, fourth, and fifth degrees of a scale. These structures help musicians convey feelings and tell stories through their compositions, making them essential for both songwriting and performance.