This article re-examines and evaluates several hypotheses regarding the way national political parties position themselves with respect to European integration. By using a pooled cross-sectional panel of data on references to Europe in the election manifestos of political parties in 16 West European countries between 1970 and 2003, I present further evidence that their stances on European integration are largely determined by their ideology, here measured by the locations of the parties within party families and their general orientation along the left/right ideological continuum. However, notable changes have occurred and the influence of ideology has diminished, as most parties have adopted more favourable positions towards the European project over time. Nonetheless, it is too early to disregard the connection between left/right and pro/anti integration, since many marginal parties are still taking oppositional stances that are strongly related to their ideological commitment.