This practice-based research employs sculptural and sound practices, and their mediation through representation, notation, technologies and performance, to develop an innovative compositional process named co-composition, in which physical and sonic material can be concurrently produced, rearranged and transformed.\nAt the core of this thesis is a multi-layered mode of thinking, informed by an understanding of emerging morphologies and the relationships formed between and across the two modalities of sound and sculpture. Taking as starting point materials and their qualities, while engaging with aesthetics and theories of minimalism and sound studies, this research seeks to introduce a co-compositional mode of creative and critical engagement, as the main research tool. Central themes are action, process, trace and time.\nMoving beyond an approach of forming analogies between modalities, this research explores a mode of navigating\nacross dimensions of sculpture and sound through a dialogue between theory and practice. The methodological approach is reflective and generative, borrowing from both traditions to develop new methods through practical exploration which emerge as part of the research process. Furthermore, analytical tools and technological mediation are employed to inform and expand how co-composition takes place in a solo environment and how this process is experienced by both the artist-performer and audience.\nThe thesis comprises a series of practical works and experimentations on co-composition, and a written text, which is critically engaging with the concepts and the progression of the research.