The area of ethnic market segmentation has received little attention from practitioners or academicians of marketing since most minority groups immigrating to the United States have gradually assimilated the cultural norms and values, and thus the market behavior, of the American society as a whole. Preliminary investigation, however, indicates that Mexican Americans are an exception. To discover whether Mexican Americans represent a true ethnic market segment of economic significance, this study examines and analyzes several aspects. First, to determine whether Mexican Americans represent a true ethnic segment, the following aspects of their cultural norms, perceptions, and values are investigated: their distinct and unique identity, the continuity and consistency of their adoption and use, and the degree of their influence. Second, to determine whether Mexican Americans constitute an ethnic market segment, grocery shopping behavioral patterns are examined. Third, to ascertain whether Mexican Americans represent a substantial ethnic market segment in terms of the number of consumers and the amount of money spent, relevant demographic and socioeconomic characteristics are presented and analyzed. Fourth, the impact of an economically significant ethnic market segment on marketers and marketing institutions is assessed. Due to the nature of this study, emphasis is placed on the collection of primary data, which has been obtained through personal interviews with 115 consumer respondents and eighteen grocery store owners and managers. Secondary data, gathered from reports of the Bureau of the Census, various periodicals, journals, and books, are used to establish cultural, demographic, and socioeconomic trends.