Western (classical) music characterises itself through the performance of so-called « works » (e.g. Beethoven’s Fifth Symphony). On closer inspection, however, these « works » turn out to be largely imaginary, ideological constructs, corresponding neither to the score nor to the reality of performance. Both early and contemporary repertoires provide different models for approaching musical compositions: in eighteenth-century partimenti as well as a twentieth-century « open works » (e.g. Stockhausen’s Klavierstück XI) performers are invited to act as co-authors of the composition. Starting from Umberto Eco’s influential definition of the opera aperta (or « open work ») this seminar will investigate different types of openness in musical compositions from early to modern, enabling musicians to rethink and reshape their mode of musical creation.