In 1959, in the wake of nearly a decade of experimentation with new forms of musical notation by composers in Western Europe and the United States, the American visual artist George Brecht began to develop a genre of text-based performance instruction he called the event score. Having turned his creative energies away from Abstract Expressionist painting and his intellectual focus from Jackson Pollock to John Cage, Brecht joined Cage’s experimental composition course at the New School for Social Research in the summers of 1958 and 1959. His notebooks from the time, selections of which are included in the Archive section of this chapter, provide an illuminating chronicle of this period. In the first pages of his notebook from the summer 1958 class, Brecht records Cage’s description of “Events in sound-space,” positing at the course’s outset an expanded field of music inclusive of all manner of multisensorial phenomena. With this definition in place, Cage’s class became an important crucible for emergent intermedia practices. There, new musical thinking was further developed by a younger generation of composers, poets, and visual artists including Brecht, Allan Kaprow, Jackson Mac Low, Al Hansen, Dick Higgins, Toshi Ichiyanagi, Richard Maxfield, and Yoko Ono. Honed under Cage’s influence, Brecht’s event score became a major genre within Fluxus, the international artist collective founded in 1962 by George Maciunas, and with which Brecht aligned himself. Brecht’s scores were frequently included in Fluxus concerts, and hundreds of Fluxus scores were written after his model. While particularly influential and broadly circulated, Brecht’s scores were not singular. La Monte Young and Yoko Ono also composed text scores beginning in the early 1960s. Because of its incredible flexibility and potential for transmission across disciplines and practices, the event score has remained a useful format for myriad conceptual, performative, and process-oriented practices from the 1960s to the present.