The current and prospective situation of cognitively impaired people entails great human, social, and economical costs. Smart homes can help to maintain at home cognitively impaired people, to improve their autonomy, and accordingly to alleviate the burden put on informal and professional caregivers. This chapter will provide a comprehensive view of the research performed at DOMUS lab. This research aims at turning the whole home into a cognitive prosthetic, especially by providing cognitive assistance. The first part of the chapter presents research on the infrastructure, both sensors networks and middleware. Research work on autonomic computing, multi-person localization, context awareness, and personalization are presented. The next part of the chapter illustrates by means of DOMUS research prototypes how cognitive assistance can help to address four kinds of cognitive deficits: initiation, attention, planning, and memory. Studies involving cognitively impaired people are also be presented. In the final part of the chapter, the role of AI, context awareness and behavior tracking are questioned. To what extend are they compulsory? Does design can provide smart and simple solutions to complex issues?