A series of three studies examined the role that social identity plays in close romantic relationships. Specifically, the concept that those in romantic relationships can and do develop a unique romantic-relationship identity with their partners is examined. The first study establishes that existing indices of group identification can be altered to assess relationship identification. Using correlations, factor analysis, and group differences between those in committed romantic relationships and those who are actively dating, Study 1 confirms the existence of romantic-relationship identity and the construct validity of the measures intended to assess this construct. Study 2 uses research findings grounded in social identity theory about how people respond to intragroup versus intergroup threats to social identity to determine whether those in close relationships respond to threats to relationship identity as they do to threats to other social identities. Study 2 determines that, in the context of romantic relationships, men generally respond to intergroup threats as social identity theory would predict, whereas women do not. Study 3 was an attempt to extend the intergroup findings for men to women. Study 3 confirms that both men and women generally respond with increased relationship identification when their partners are criticized on an important dimension, such as intelligence. The possible moderating roles of adult romantic attachment and self-esteem are explored. Finally, implications for theory and research are discussed.