Two studies establish distinct types of social and collective identities (Study 1) and describe dimensions that differentiate among identities (Studies 1 and 2). In Study 1, individuals (N = 50) sorted 64 social identities on the basis of perceived similarity; 259 respondents provided trait property ratings of the identities. Cluster analysis indicated 5 types of social identity: personal relationships, vocations/avocations, political affiliations, ethnic/religious groups, and stigmatized groups. Multi-dimensional scaling analysis shows that identities differ on several trait properties, including desirability and collectivity. In Study 2, 171 people rated the similarity of identities within a specific cluster; 193 respondents provided trait property ratings. Results indicate that different trait properties are relevant to each cluster. The theoretical importance of distinguishing among forms of social identification is stressed.