This book offers both an introduction to the theory of Western music, focusing on the period from 1650 to 1900, and a scientific exploration of the acoustical principles behind its production. Readers will be guided through fundamental concepts such as chords, tonality, modulation, and chromaticism, with particular emphasis on the role of harmonics in musical sound. By the end of the book, they will have gained a valuable set of tools to deepen their understanding of music theory and composition, enabling them to create meaningful and innovative music for the listeners of tomorrow.