Interactive adaptive systems increasingly become part of our everyday life. Which factors could shape this development and under which conditions will interactions with technical systems be deemed socially appropriate? The " FA ctors of  S ocial  A ppropriateness" (FASA) Model presented in this Open Access-book provides a structured approach to our understanding of social appropriateness in human-technology interaction. The FASA Model serves to inform design choices for sociosensitive and socioactive artificial assistants.