In the past 70 years, various composers have composed so-called poly-works, that consist of at least two works that can be performed either independently or simultaneously. If the simultaneity is intended during the compositional process, it affects the structure of the pieces and also their relationship to each other. This raises the question of how the entanglement of the pieces is organized. It furthermore draws attention to the aesthetic conditions and formal categories. So far, the concepts of poly-works and simultaneous performances and their potential impact have rarely been studied. Focusing on the different possibilities of entanglements, the thesis reveals different types of interrelationships and interdependencies between the individual pieces. These different types are introduced as a new interformal level, linking and relating the different works in a vertical mode. Technically, this vertical linking recalls an important feature of the principle of polyphony, which is the combination of different, highly independent lines. In poly-works this combination is extended from the material form of a piece to an overall concept of a meta-work. Different work identities complement each other to form a new work-entity and thereby offer different refined perspectives on the musical text. With form giving up its claim to absoluteness, this might, however, create an ambiguity between the different roles and functions that a piece can assume. This goes along with an extension of the scope for interpretation. Aesthetically, this ambiguity recalls an important feature of the open form. Both, the concepts of polyphony and the open form are considered and rethought in regard to the special cases of multi-level work constellations and performances. Their hybrid nature exhibits the characteristics of individuality and independence as well as the feature of socialization. In this sense, poly-works can be regarded as a new spatial-temporal concept, exploiting the ability of simultaneous perception and reflecting on modern life and socialization.