Europe is aging - people are living longer and fewer babies are being born. This has important implications long term, as there are fewer people to care for older people, and also fewer people working to finance their care. One solution that has been proposed is Ambient Assisted Living (AAL) - new technology that allows people to stay in their own homes longer and may also support carers, thereby reducing the economic impact on society. Despite extensive funding in Europe to support the development of AAL systems starting in 2008, there are not many systems on the market, making it interesting to understand why. This research studied the development of these systems, as this is where decisions about functionality and design are made that can affect user acceptance and success on the market later. The goal was to identify issues teams face and to gain understanding of these. ^The approach of studying development processes has been successfully applied previously in other research areas to gain insight. Taking a Human-Computer Interaction perspective, a key focus here was the way in which the needs of the people who will use the system were gathered and taken into account during the development process, but also wider issues were considered. Qualitative methods were applied to explore this topic. Two large case studies of projects developing AAL systems were conducted. The rst involved a tablet based system that was studied during the development itself. The second case study considered a project that developed a more comprehensive smart home system in retrospect. Both projects aimed to combine monitoring fea- tures to increase security in private homes with interactive services to support older people. ^These case studies provide detailed accounts about what occurred during these projects, which started out user-centered and yet did not reach their goal of having a successful product. To expand on these results and check whether these issues have also been experienced by others, a series of studies was conducted that included a wider group of people with experience developing AAL systems. For this purpose, interviews, workshops and an interactive poster were done. These supported finding further issues, but also getting suggestions about how to address some of these. The findings point to issues around the complexity of the term 'user' in these types of systems, how sensors frame notions of the user, the hidden effort to get systems working, and the impact of funding arrangements on projects. While some of the issues found are intrinsic to the problem space, others are within the control of teams and can be addressed with available methods and good project management. ^Yet others point to problems that warrant further study, both to gain further understanding and to develop appropriate solutions. AAL is an important area for the future. The results provide a basis on which to build more successful systems, that are both reliable and usable, in the future.