The individualism and collectivism constructs are theoretically analyzed and linked to certain hypothesized consequences (social behaviors, health indices). Study 1 explores the meaning of these constructs within culture (in the United States), identifying the individual-differences variable, idiocentrism versus ailocentrism, that corresponds to the constructs. Factor analyses of responses to items related to the constructs suggest that U.S. individualism is reflected in (a) Self-Reliance With Competition, (b) Low Concern for Ingroups, and (c) Distance from Ingroups. A higher order factor analysis suggests that Subordination of Ingroup Goals to Personal Goals may be the most important aspect of U.S. individualism. Study 2 probes the limits of the constructs with data from two collectivist samples (Japan and Puerto Rico) and one individualist sample (Illinois) of students. It is shown that responses depend on who the other is (i.e., which ingroup), the context, and the kind of social behavior (e.g., feel similar to other, attentive to the views of others). Study 3 replicates previous work in Puerto Rico indicating that allocentric persons perceive that they receive more and a better quality of social support than do idiocentric persons, while the latter report being more lonely than the former. Several themes, such as self-reliance, achievement, and competition, have different meanings in the two kinds of societies, and detailed examinations of the factor patterns show how such themes vary across cultures. This article contains two parts. Part 1 presents a theoretical analysis of the constructs of individualism (e.g., de Tocqueville, 1946) and collectivism, including a discussion of the probable antecedents and consequents of the emphases on these values in different cultures. Part 2 presents three studies. The first study, based on U.S. data, provides attitude items that can be used to measure the individual-differences dimension ailocentrism versus idiocentrism. Ailocentrism versus idiocentrism is a within-culture variable that corresponds to collectivism versus individualism at the cultural level. The second study tests the limits of the constructs, with data from Japan, Puerto Rico, and Illinois. The third study replicates previously obtained (in Illinois) findings with data from Puerto Rico that allocentric persons report receiving more social support and a better quality of social support, and idiocentric persons report higher levels of loneliness.