This article presents a critique of the commonplace trope that holds genre to have declined in relevance under modernism. Contrary to the widespread notion that composers’ repudiation of received tradi- tion rendered the very idea of genre categories obsolete, this article argues that such categories have never ceased playing a decisive role in the production, circulation, and reception of post-1945 art music. In interrogat- ing the assumptions that underpin the “decline-of-genre” thesis, this article underlines the utility that renewed attention to genre and its framing effects may have for the analysis of this repertoire. To this end, an alterna- tive to standard theories of genre is advanced, one that draws on actor-network theory to destabilize catego- ries too often conceived as fixed, solid, and binding. This revised theory of genre is applied to Gérard Grisey’s six-part cycle, Les espaces acoustiques (1974–85). Habitually regarded as an exemplar of spectral music, Grisey’s cycle may be understood as participating in a number of additional generic contexts at the same time. Taking such generic overdetermination into account not only sheds light on the range of conflicting interpreta- tions that Les espaces acoustiques affords but also suggests how music analysis might better address the heterogeneous contexts and multiple listener competences that this and other musics engage.