Ubiquitous computing implies that literally any activity in everyday life can be assisted or accompanied by networked computers. Therefore, the concepts of everyday social life must be carefully reflected on when developing applications for ubiquitous computing. The present chapter focuses on the concepts of trust and accountability. First, both concepts are introduced with their everyday semantics. Second, we explain why trust is relevant for ubiquitous computing, and introduce the main issues for dealing with trust in computer science. Third, we show how accountability can be achieved in distributed systems using reputation and micropayment mechanisms. In both sections, we provide a short overview of the state-ofthe- art and give detailed examples for a deeper understanding. Finally, we provide a research outlook, again arguing for the integration of these concepts into future ubiquitous computing applications.