xv Preface Due to increased life expectancy and improved general health states of citizens, more and more old and frail people will need medical care in the near future. At the same time, considerable bottlenecks arise from the fact that increasingly fewer people are present, who may take over the nursing. In order to master the requirements of an aging society, innovations in information and communication as well as medical engineering technologies come to the forefront, which offer novel or improved medical diagnosis, therapy, treatments and rehabilitation possibilities. Nevertheless, recent research shows that acceptance barriers are prevalent, which might be due to the fact that current development praxis predominately focuses on technical feasibility, while the "human factor" in these systems is fairly underdeveloped. In order to fully exploit the potential of future healthcare applications, acceptance and usability issues of assistive technologies need to be considered, especially for older users, who have specific needs and requirements regarding usability and acceptance issues. As the knowledge about the antecedents