This document is the introduction to a harmony textbook. It discusses the relationship between melody, harmony, and the overtone series. It explains that harmony takes root in melody, as polyphony developed from simultaneous melodic progression. It then discusses the harmonic series and how the notes in the diatonic scale can be related to intervals found in the overtone and undertone series, but these series alone do not fully explain the scale. The introduction provides background on harmony and its foundations in both melody and the harmonic series.