A defining characteristic of democratic regimes is that they depend on widespread popular approval of domestic and foreign policy choices made by their elites. This article examines the sources of East European public support for NATO membership. It argues that citizens' attitudes in favor of participation in the North Atlantic defense system are affected, at the individual level, by their own values and characteristics, and at the aggregate level, by the national past experience and the domestic political context. The hypothesized effects of micro- and macro-level factors are tested through logistic regression analysis of data from the 1995 Central and East European Barometer Survey. The results suggest that perceptions of threat from Russia developed in nations occupied by the Soviet Union at the beginning of World War II and the ex-Communists' access to government are factors which mould public opinion and explain differences across countries. Pro-integration and pro-market attitudes emerge as influential determinants of NATO approval which account for the variation observed between individuals. These findings and their theoretical and practical implications are discussed in the context of the recent eastward expansion of NATO and the Kosovo crisis, demonstrating the need to study the dynamics in East European popular appreciation of foreign policy choices over time.