Categorization is integral and essential to human social interaction (Allport, 1954; Chaiken & Trope, 1999; Fiske & Neuberg, 1990). We classify and categorize without, for the most part, giving it a second thought-but it is crucial for our successful navigation of social life. As journalist Gary Younge notes above, our multiple identities are not simple, neutral, passive definitions of our existence; they are laden with implied status, power and value, and therefore of profound consequence for our lives. Categorization is dynamic and fluid-and we can both choose to be categorized, or categories can be chosen for us. Whether we are talking about being black or white, male or female, young or old, such social classifications have significant implications for how we think about ourselves and form impressions of others. In any given situation the categories that define ourselves, and others, can depend on various factors, such as context (e.g., Oakes, Turner, & Haslam, 1991) and motivation (e.g., Sinclair & Kunda, 1999) and increasingly it is apparent that

in many contexts multiple bases for social categorization can be salient, combined and used simultaneously (e.g., see Brewer, Ho, Lee, & Miller, 1987; Stangor, Lynch, Duan, & Glass, 1992). This volume discusses how our classification of ourselves, and others, along these multiple criteria, can impact on psychological and social processes.