Every year, thousands of undocumented Mexican workers enter the United States. Their presence, together with the settlement of undocumented and legal immigrants from many other countries, constitutes the source of one of the most persistent ideological conflicts in American history: the conflict over immigrants' rights. Official discourses in many cases identify being Hispanic with poor performance at school, drug abuse, poverty and violence. However, aside from mainstream images of who immigrants are, little research has been done on the identity that immigrants themselves build and project, and on the processes that affect the formation of such identity. In this article I investigate identity through discourse analysis, looking specifically at linguistic strategies used by a group of undocumented Mexican immigrants to identify characters in storytelling. I argue that immigrants use ethnic identity as a central identification category for self and others in their stories, showing that ethnic mentions are widespread in story orientations, and that they exhibit different degrees and types of relevance depending on their relationship with the interactional context and/or the story world. Ethnic mentions are used in stories to affirm certain characteristics of one's own identity and of the identity of others via the presentation and evaluation of behaviors. In argumentative stories disputable behaviors are openly attributed to out groups, and so these stories help speakers to build images of who they are and how they stand in relation to others. In stories of personal experience, the connections between identities and behaviors are implicit, but they still respond to socially established expectations. Thus, individual stories also contribute to build those expectations about how belonging to certain ethnic groups may affect action in particular domains of life. The pervasiveness of ethnic identification in immigrant stories cannot be understood without resorting to wider social processes that frame the immigration experience of undocumented Mexican workers. In this case, I stress the importance of the pressure that the ideology of race and ethnicity, enacted through public discourse at all levels, exerts on every individual in American society.]