Our purpose in this article is to cross-validate expert and manifesto measures of party positioning on European integration. We compare these data with each other and with measures from a European election survey and an elite survey of parliamentarians. We find that expert surveys provide the most accurate data for party positioning on European integration. In part, the errors of expert evaluations and electoral manifestos are shared. Both have some difficulty measuring the positioning of small, extreme, parties. But we also detect and explain errors that are unique to each measurement instrument. © 2006 Elsevier Ltd. All rights reserved.