Through a combination of theoretical and historical analysis, the author develops the thesis that the concepts of "race" and "ethnicity" are socially constructed. With case studies of the incorporation of Blacks and Irish immigrants into the social structure of the United States, Richard Williams demonstrates that the social values that have been placed on these groups result from their placement into specific labor categories rather than from attributes inherent to the groups. The author first analyzes the process by which the social identities of Blacks and Irish developed in their native lands. Turning to an analysis of the social structure in the United States at the nation's founding, he argues that the society was hierarchical from its inception and that Black slave laborers and Irish wage laborers were demanded to fill positions created by that hierarchical structure. The conceptions of their racial and ethnic identities developed through a transfer of the value assigned to their social positions to the groups themselves. Racial and ethnic identities represent, the book argues, the legitimization of social stratification based on power relations.