English abstract Material Matters in Co-designing Participation in design is broadening, and there is a movement away from designing to co-designing. They are related, but the little co- makes them different organizational and socio-material practices. Practically, co-designing typically takes place in multidisciplinary, distributed, complex projects, where people – and invited materials – only occasionally meet, align and make each other act, in the situation at quite explicitly staged co-design events. With a broad view of materiality and focus on co-designing as processes, this work suggests ways of understanding and staging a co-designing practice, which entails a move away from a focus on methods and pre-designed proposals, towards an acknowledgement of participating materials and formatting co-designing. This calls for additional ‘material’ (broadly understood) of the co-designer, including skills of drawing together and delegating roles to non-humans as parts of staging co-designing with others. Further, it necessitates a different understanding of co-design processes from what can be efficiently managed to materially staging performative co-designing. This practice-based, programmatic and materially interventionistic work builds upon and draws together about ten years of engaging with hundreds of people and materials in many co-design networks, projects, events and situations, through five experimental, participatory design research projects, teaching and other co-design ‘workshop’ series. Partly in opposition to the ‘classic’ design field of industrial design, the thesis intends to contribute to the (co-) design fields of interaction design and especially participatory design, but also to co-creation and service design.