The EU's 'social dimension' today is a product of the ideology of the 1990s. Its employment field is directed to increase the employability of workers and the adaptability of labor market regimes. The book argues that this social-liberal approach is best explained with a set of ideas strategically advanced by 'thought communities' in the policy process. It traces the success of this new approach in the debates among academic experts and policy-makers in the mid-1990s, the decisions leading to the adoption of the Treaty of Amsterdam, and the establishment of the approach in the policy field between 1997-2007. The author explores the processes through which ideas came to matter in the policy process. At every stage, the claim that ideas played a predominant role is strengthened by addressing the most viable alternative explanations such as institutional constraints set by Economic and Monetary Union and the preferences of political leaders