The bonds that connect each person to important others, whether individuals (e.g., friends, romantic partners, close kin) or social groups (teams, workgroups, national or religious groups) are a core conceptual focus of the field of social psychology. Historically, research on personal relationships and research on in-group ties have proceeded as two largely independent streams. Recently, theorists and researchers have recognized the strong conceptual parallels between these issues and have moved to take advantage of them (Sedikides & Brewer, 2001; Smith, Murphy, & Coats, 1999; Smith & Henry, 1996).

In both areas, two phenomena are of central importance. One is the influence of a personal relationship or significant group membership on people's thoughts and feelings about themselves – an effect of the other person or group on the self. For example, when a social group membership becomes salient, people tend to see themselves in terms of the typical or stereotypical characteristics of the group rather than in terms of their unique personal identities, a process known as depersonalization (Turner et al., 1987). Conversely, the second phenomenon is the influence of the self on thoughts and feelings about the other person or group. For example, people tend to project their own individual characteristics (e.g., their attitudes and preferences) onto other group members, assuming that those others are similar to themselves (Robbins & Krueger, 2005).