We develop a novel optimization approach to tone. Its grammatical component consists of the similarity- and proximity-based correspondence constraint framework of Agreement by Correspondence theory (ABC). Its representational component, Q Theory, decomposes segments ( Q ) into temporally ordered, quantized subsegments ( q ), which comprise unitary sets of distinctive features, including tone. ABC+Q unites phonological alternations and static lexical patterns, as we illustrate with a programmatic survey of core tonal phenomena: assimilation, dissimilation, lexical tone melodies, and consonant-tone interaction. ABC+Q surmounts long-standing problems for autosegmental-era, multitiered representational approaches to tone, and unites tonal and segmental phonology under the modern umbrella of correspondence theory.