Originally published in Die Reihe, 1978; later published in Monograph, Institute for Studies in American Music, 1979.
Ionisation (1930), as we now recognize it, is the first and the most consummate work to explore the structural value of all non-pitch properties of sound without electronic means. It is also unique in Varèse's output. In Ionisation, more than in any other score, Varèse reveals to an extraordinary degree not only his concepts and techniques but also the profundity and imagination with which he crystallizes (to borrow one of his own favorite expressions) his ideas: in this case, hewn from raw sonic material that offers no definite pitch or known means for development and organization. To analyze Ionisation, then, is to pave the way for understanding all of Varèse's music.
The first step in understanding Ionisation’s structure is to analyze Varèse's choice of instruments. Initially, these instruments can be classified into the following seven categories according to timbre:
All instruments in Ionisation are assigned one or more of the following functions:  generating germinal ideas,  defining textures,  linear elaborations,  verticalization of textures,  delineating phrases and sections,  “modulation” in timbre and register, and  providing special acoustic characteristics.