Personalization and autonomous adaptation to users has become a mainstream feature. The diversity is immense, and spans domains ranging from personalized online search and recommenders, to social robots. Based on the findings of a set of studies of people’s responses to autonomous and adaptive systems, and current commercial developments, I highlight a number of challenges related to user trust in such systems, focusing on transparency, social strategies and social mediation effects. Rather than focusing on convincing users to use systems, a more pressing challenge is how we can increase awareness and understanding of the autonomous and user-adaptive systems already there.