Managers are more and more interested in social networking sites because they provide opportunities for strengthening relationships with customers as well as site content and service. Using social networking sites effectively, however, depends on understanding both the psychological attributes and social interactions of participants. This paper addresses these topics by presenting the results of a two-study inquiry into the importance of two personality traits (consumer innovativeness and expressiveness) to active and passive use of social networks among Italian consumers. In Study 1 (n = 753) it was found that innovativeness is positively related to active and passive use. Study 2 (n = 277) revealed that self-identity expressiveness and social identity expressiveness positively influence only active use. These results suggest that managers need to distinguish bet-ween, and differentially encourage, joining and browsing such sites on the one hand and actively contributing to them on the other. Managers can also enhance the impact of their social networking sites by taking into account social and self-identity expressiveness to increase affiliation and market share and by encouraging consumers to use these sites actively.