Don Carlo Gesualdo, Prince of Venosa, (1566–1613) is celebrated for his idiosyncratic use of chromaticism. Yet, the harmony of Gesualdo's madrigals evades modal rules and his chromatic style has perplexed analysts. This thesis reappraises the modal and chromatic features in his madrigals and expands on their significance by employing pitch-class set theory analysis to enhance a more traditional modal approach. Whilst analysis of the music through modal features and pitch-class set theory may appear to use contradictory analytical methods, the two can complement each other through the recognition of certain interval patterns regarded as significant by cinquecento music theorists. Ultimately, this analytical technique provides a language with which to articulate the modal and chromatic processes occurring in his music. In order to consolidate the results of the analyses, elements of compositional process are delineated and explored in the dissection of the madrigal '"Io parto" e non più dissi.'