Online trust is one of the main determinants of the success of e-retailers and much research has dealt with website features triggering consumer trust to them. Another stream of research focuses on the psychological antecedents to online trust; i.e., what “happens” in the consumer’s mind before or while a person decides to trust an e-retailer? so far, each effort has focused on only a few selected aspects of this trust formation process. No study has attempted to identify major psychological antecedents of trust. Our work identified the relative importance of the antecedents of institution-based trust in e-retailing; i.e., trust people have in it in general. A review of the literature reveals a large number of potential psychological antecedents. These can be categorized into five group of factors: personality-based, perception-based, attitude-based, experience-based, and knowledge-based. The five categories are hypothesized to influence institution-based consumer trust in e-retailing. According to our results, perception based factors are the main determinants of consumer trust in e-retailing. Consumers do behave, after all, rationally.