East–West union co-operation in Europe is discussed as the most serious test to cross-border union solidarity, in the light of new frameworks capable to make sense of transnational trade union activity and alternative to theoretical nationalism. The empirical assessment of trade union chances reviews the activities of trade unions in the UK, Germany, Austria and Poland on foreign investment, migration and movement of services. Secondary evidence and case studies show that the strength of transnational union action does not depend on the country, but rather on its form. ‘Structural’ Europeanization remains weak (e.g. in most European Works Councils), while network-based action is displaying strong developments, especially on migration, but least on the movement of services.