The major hypothesis of this article is that attendance at interparliamentary group meetings by members of Congress between 1949 and 1970 modified their attitudes toward foreign policy. Interviews with a sample of congressional delegates, analysis of roll call data, and documentary records were used to test this hypothesis. Changes after attendance at an initial meeting were small. However, when party, ideology, and degree of previous isolationism or internationalism were controlled the changes were much more significant. Predictions formulated on the basis of cognitive dissonance theory were remarkably accurate, thus suggesting that cognitive consistency explanations may help to account for the behavior observed.