While the question how community design influences user behaviors in online communities has recently attracted considerable research, few studies empirically evaluate the influencing factors of specific user behaviors. Building on Ren et al.’s (2007) conceptual framework of identity-based vs. bond-based attachment in online communities, this study evaluates the influence of numerous antecedents on user attachment as well as attachments’ mediating role for explaining consumer behavior. Using data from a large-scale survey, we find that network effects, intergroup comparison and social categorization have a positive and significant effect on common identity attachment while this is not the case with in-group interdependence. Conversely, common bond attachment is driven by collectivism, interpersonal similarity and social interaction, while personal information has no effect on common bond attachment. Most importantly, the analysis results show that common identity attachment is the primary driver for user behaviors in online communities.