The instrumental theater of Mauricio Kagel is one of the most significant phenomena in the realm of new music theater and continues to influence it today. In the early years, between 1959 and 1965, Kagel systematically explores, through various experimental setups, how the relationships between the audible and the visible can become subjects of composition. This book provides a comprehensive presentation of this early instrumental theater: the phenomena are placed in a historical context, with a particular emphasis on Kagel's aesthetic socialization in Buenos Aires during the 1940s and 1950s. The individual compositions are described, and the fundamental motives of an aesthetics of instrumental theater are developed. A central focus is also on how the analyses can account for the fact that in Kagel's instrumental theater, the visual dimension holds structural significance and that Kagel composes intermedially. Finally, the author was able to include the entire sketch material for this book for the first time, offering a completely new perspective on Kagel's compositional process.