This book addresses the (re-)emergence of labour Euroscepticism. Comparing fifty years of Italian and Irish unions' changing preferences towards the EU from 1950-2015, Labour Euroscepticism sheds light on why unions' stances towards European integration changed over time. Of critical contemporary importance is unions' capacity to locally police increasingly transnational labour markets. Hence, the book points to labour politics in general, and different industrial relations systems in particular, as being critical to better understanding the growing Euroscepticism of unions and workers. Darragh Golden posits that the likelihood of unions' continuing support for European integration is contingent on their 'coping mechanisms' in a transnational labour market. This book shows that labour Euroscepticism has sociological rather than ethno-culturalist roots. By drawing on in-depth empirical research, the book thus goes beyond methodological nationalism and culturalist explanations, both prevalent in current scholarship on European integration.