DescriptionExpanded chords—those comprising five notes or more and a variety of intervals including thirds, fourths, fifths, seconds in diverse combinations—are at the center of Charles Ives’s compositional and philosophical thought, functioning both as a byproduct and as a generator of other ideas. In addressing Ives’s eclectic compositional techniques, other scholars have generally addressed the role of expanded harmony as a subtopic within other issues. This dissertation, in contrast, treats extended harmony as a ubiquitous presence in Ives’s music and as a unifying factor for various ideas discussed by other scholars. After discussing Ives’ harmonic influences, I trace the use of expanded chords in a variety of works—[Grantchester, Ann Street, The Things Our Fathers Loved, Central Park in the Dark, Psalm 67, Concord Sonata and others]—as they relate to issues of philosophy, programmaticism, and form.