When Professor Joe Lee wrote his magisterial history of twentieth century Ireland in the late 1980s one of the most important issues he addressed was the apparent economic failure of the Republic of Ireland. The main reasons advanced for this failure included slow and erratic patterns of economic growth, low productivity in key economic sectors, high and persistent levels of unemployment, exceptionally high emigration rates and a preponderance of enduring social problems. That this remained the case after more than a decade of EU membership seemed to call into question the wisdom of the Irish decision in 1973 to join the then European Community (EEC). Two decades later Ireland’s membership of the EU was thrown into serious question by the Irish electorate’s rejection in June 2008 of the Lisbon Treaty. This was the third such referendum on Europe held in Ireland since the millennium and the second referendum in three to result in a rejection of an EU Treaty following the failed Nice poll in 2001 (O’Brennan, 2003, 2004). The debate on the Lisbon Treaty offers the opportunity to look back at and reflect on Ireland’s membership of the EU, to examine whether and to what extent membership has been good for Ireland, and the fundamental changes which European integration has wrought. And although the No to Lisbon was reversed in a second referendum held in October 2009, it remains the case that European integration is now seriously questioned in Ireland. This chapter examines the Irish experience of European integration. It assesses the impact of the EU on key aspects of Irish economic and political life and the different modes of adaptation and contestation which have characterised the Irish experience of membership.