The current “cultural turn” in the study of social movements has produced a number of concepts formulating the cultural–symbolic dimension of collective actions. This proliferation, however, has resulted in some confusion about which cultural–symbolic concept is best applied to understanding cultural processes involved in social movements. We articulate a new definition of ideology that makes it an empirically useful concept to the study of social–movement mobilization. It is also formulated as autonomous of concepts such as culture and hegemony and of other cultural–symbolic concepts presently used in the movement literature to explain participant mobilization. We demonstrate the usefulness of our ideology concept by analyzing letters written to Martin Luther King, Jr. from segregationists opposed to the integration of American society. The analysis indicates that the letter writers particularized segregationist culture, creating ideologies that fit their structural, cultural, and immediate circumstances, and that the ideologies they constructed thereby acted to mobilize their countermovement participation. The particularizing resulted in four differentiated ideological versions of segregationist culture. The empirically acquired variety of ideological versions is inconsistent with the role attributed to cultural–symbolic concepts in the social–movement literature and requires theoretical clarification. We conclude with a discussion of the theoretical implications for social–movement theory of the variety of segregationist ideologies.