This essay investigates the ways in which Tony Williams's fusion band, Lifetime, challenged and complicated the meanings jazz held as both a tradition of popular music and as art music. The band merged psychedelic and hard rock styles with jazz, producing music that unmasked the racialized assumptions behind genre categories, helped introduce rock's enthusiastic use of new recording technologies as aesthetic ends in themselves to jazz recordings and performances, and fomented an explicit engagement with young, popular audiences. Lifetime's accomplishments were produced in spite of music industry misunderstandings about the band's music as it did not easily fit into given generic categories, jazz audiences' resistance to their music because of its unapologetic embrace of rock aesthetics, and jazz critics' antipathy towards rock music more generally. As young musicians who had grown up appreciating rock music as well as jazz music, the members of Lifetime helped initiate the formation of a set of musical practices that operated under a number of different names but which I call “fusion music” in order to highlight the explicit generic mixing these young musicians enacted. One of Williams's primary motivations for merging rock and jazz was to reach beyond normative genre categories, evincing the naked, perhaps naive, optimism fusion held for its early practitioners.