Scholarly studies on John Adams's music routinely adopt Timothy A. Johnson's theoretical model, the common-tone index (CTI), working with the premise that Adams's building blocks are triads "formed by thirds superimposed by a root." My study aims to broaden the gamut of harmonic structures in Adams's musical works by using a jazz-oriented approach. Adams's first piano concerto, titled Eros Piano, represents his first overt attempt to infuse jazz elements within his own compositional style. I will explore this concerto and provide an overview of other works that bear some affinity to jazz pertaining to chordal voicing, dominant- seventh cycles, rootless chordal formations, tritone substitutes, and other idiomatic jazz voicings. Next, I will examine the interaction of harmony and melody using chord-scale theory. In conclusion, I will consider the implications of Adams's infusion of jazz elements within his oeuvre to untangle notions of minimalism, postminimalism, and other artistic paths Adams has sought throughout his compositional career.