Abstract The concept design of small handheld electronic and telecommunication devices is a creative and dynamic process. Interaction between the designers plays an important role in the creation of new products. This thesis addresses the communication between product concept designers. The aim of this thesis is to examine new ways of developing computer systems for remote collaboration. Multiple research methods have been used so as to enrich the view of the research subject. Product concept design has been studied in field studies and at co-located concept design workshops where the object of design was uncertain. Co-located workshops were organised to examine the moment to moment interaction between designers to discover how designers collaborate when designing a design object in common. By applying the concepts of activity theory, the concept of instrument is elaborated. Four types of instruments to mediate between a designer and the object of design and collaborating designers are identified. These are the instruments used to externalize an understanding of the design object, the concrete means of interaction, the future artefact and the hypothetical user activity. The latter two make up the design object which designers' strive for, and can also be instruments for scaffolding each other. A conceptual model was developed to describe the design action and the instruments for collaboration. This model was used to gain insight into the creation of computer support for remotely collaborating designers by posing questions for computer systems design. To develop computer systems to support designers in remote collaboration, an understanding of both the requirements set by the field and the technological feasibility is needed. Three application prototypes are presented as proof of the concept and as an experiment with virtual prototyping technology. The concept of design action has been defined on the basis of activity theory. Computer-supported geographically distributed workshops have been organised and analysed using the design action as an analytical tool for the research material. I conclude that, in order to support remote collaboration of concept designers, computer systems should support collaborative construction of the object of design. Instruments, such as the future artefact, its various representations and the conceptual construct of hypothetical user activity are potential instruments for computation.