One problem many organizations deal with is how to effectively govern their online communities. Unlike employees, online community members often respond poorly to formal control mechanisms. This study develops theory on how moderators can build norms in online communities using frame analysis theory from the social movements literature. Through a case analysis of two communities focused on discussing recreational drugs, our findings demonstrate that norm formation is influenced by two phenomena: (1) norm acceptance, and (2) norm transience. Norm acceptance requires that moderators be consistent in their expression of norms. To a lesser extent, moderators must be credible in their expression of norms. If these things occur, the community will accept the norms. Norm transience, on the other hand, occurs when moderators are not sensitive to the community identity. If accepted norms are not aligned with community identity, they will be dropped by the community within one or two years.