While the literature on public support for European integration often suggests that political elites play an important role in shaping public attitudes toward the European Union, the empirical findings to date reveal an inconsistent pattern of political effects. The causal direction of this relationship has also been questioned. Using data from the Eurobarometer surveys, this article tests hypotheses to explain national, partisan, and individual-level variations in the strength of the party/voter connection. The results of a nonrecursive model demonstrate that party positions do influence electorate opinion, but that this effect varies with levels of disagreement among parties, party unity, issue salience, and party attachment. These results help to explain when and where political parties will exercise the greatest influence over public opinion.Early research on European integration often described a process insulated from public opinion by the obscurity of intergovernmental negotiation and an elite consensus in favor of integration. With the expansion of the scope of EU policymaking, European integration has become more controversial and salient. The concomitant increase in treaty revisions, with their attendant referenda, gives public opinion a powerful direct role in constraining the future development of the EU.A number of authors writing on public support for European integration have argued that political elites exert a formative leadership over mass opinion. Hypothesized political influences have been found by some studies, and rejected by others, giving rise to ad hoc speculation about the conditional nature of political effects. This article will evaluate several arguments found in the literature on public support for European integration as well as theories drawn from the psychological literature on persuasion. The results indicate the conditions under which political parties can be vital factors in shaping public opinion. 1