This study examines political party contestation over Europe, its relationship to the left/right cleavage, and the nature and emergence of Euroscepticism. The analysis is based on a large original sample of parties’ claims systematically drawn from political discourses in the mass media in seven countries: Britain, France, Germany, the Netherlands, Italy, Spain, and Switzerland. It addresses questions concerning parties’ mobilized criticisms of European integration and the European Union (EU), specifically: their degree and form; their location among party families and within party systems; cross-national and diachronic trends; their substantive issue contents; whether their ‘Euro-criticism’ is more tactical or ideological; whether claims construct a cleavage; and their potential for transforming party politics. Findings show that a party’s country of origin has little explanatory power, once differences between compositions of party systems are accounted for. Also governing parties are significantly more likely to be pro-European, regardless of party-type. Regional party representatives, by contrast, are significantly more likely to be ‘Euro-critical’. Overall, we find a lop-sided ‘inverted U’ on the right of the political spectrum, but this is generated entirely by the significant, committed Euroscepticism of the British Conservatives and Schweizerische Volkspartei. There is relatively little evidence for Euroscepticism elsewhere at the core, where pro-Europeanism persists. Finally, parties’ Euro-criticism from the periphery mostly constructs substantive political and economic critiques of European integration and the EU, and is not reducible to strategic anti-systemic challenges.