Population ageing and increased digitalization each constitute an ongoing and profound transformation within contemporary modes of living, as growing advances in technological development mix and intermingle with the lived realities of older people as the final recipients. It is against the backdrop of this interplay that user involvement has enjoyed ever-rising advocacy to an almost normative degree. Beyond articulating methodological principles, however, the literature has remained surprisingly vague as to the practical implementation of the approach. Less appears to be known, (...) both empirically and conceptually, about how design and user involvement are done in practice and how they would matter to bring about intentional or unintentional effects. To engage with these developments, this thesis aims at taking the practices of user involvement and design to the centre of its inquiry by adopting a perspective from Science and Technology Studies. Specifically, the thesis seeks to both build on and contribute to the established body of STS on the connection between technology design and older users and ask: What is there to learn about user involvement as a method, if we focus on the practices of doing user involvement? To answer this question, the thesis studies four different aspects of the practices of user involvement and design. In particular, the thesis reviews the literature on how user involvement mattered in previous empirical projects that include older people, it examines how different configurations of participation matter in design workshops, it scrutinizes the achievement of user involvement in corporate practices and it traces the circumstantial performances of such practices. The largest empirical piece comes from a two-year ethnographic study of a small- to medium-sized enterprise, the material from which informed Paper III and Paper IV. The findings highlight how user involvement in practice is both contingent and transformative, as it selectively enrols different participants and performs multiple realities. In practice, user involvement appears to be dependent on a set of underlying premises and socio-material conditions and thus is always a dynamic and momentary achievement. Furthermore, the thesis shows how the practices of user involvement themselves may bring into existence different realities, articulating and materializing particular versions of objects and images of ageing. Accordingly, the thesis contributes theoretically by illuminating the underlying socio-material facets of user involvement, and by emphasizing ageing as a particular object/image of design. Specifically, the appended papers encompass a conceptual framework, as well as three new concepts: design multiple, shifting interstices and viscous image landscape, in order to theorize the underlying conditions for user involvement, its relationship with design and its entanglement with ageing. Practically, the thesis enunciates three main implications regarding questions of goodness, politics and ethics. (shrink)