The purpose of the present study was to examine media fandom participation from a social identity perspective. Prior to the main study, a new measure of media fan identification was created and internal reliability was established. For the present study, a total of 261 self-proclaimed Harry Potter or Twilight fans were assigned to receive affirming or threatening feedback about their fan identity, and then participated in a fandom-related task. Highly identified fans whose fan identities were affirmed showed greater engagement in the fan task compared with threatened and weakly identified participants. These findings indicate that media fandoms operate in a manner similar to other social groups, with members of average and above average levels of group identification demonstrating sensitivity to group categorization and the psychological benefits and costs of engaging with their chosen media fandom.