Computer usage today is predominantly based on graphical interaction, where the visual presentation of information is essential both for input (hand-eye coordination when using a computer mouse), and output (seeing the information on a computer screen). This can create difficulties for blind computer users, both at an individual level when interacting with a computer, and also when collaborating with other computer users. The work presented in this thesis has investigated interaction for blind computer users in three stages. First investigating access to information by making studies on an interactive audio-only game, drawing conclusions about auditory direct manipulation and auditory interface design. Second studying collaboration between blind and sighted computer users in two different contexts, leading to questioning of commonly expressed design principles regarding access to collaboration. Finally studying accessibility in a working environment, finding out how technology, the assistive device used by the blind person, communication with others and professional knowledge interplayed to create an accessible work environment. Based on these empirical studies, the main conclusion from this work is a proposal of a research perspective, Assistive interfaces as cooperative interfaces. Here, the context where the interface is going to be used is in focus, and cooperative and social dimensions of interaction are acknowledged and highlighted. The design and analysis of assistive devices should be highly sensitive to the socio-interactional environment, and not just focusing on the single individual using an assistive device. / QC 20100921