Approaches focusing on ideological and cognitive factors to analyse public policy have moved to centre-stage in political science. This book presents the great variety of theoretical and empirical research on the role of ideas which has emerged in recent years. How can you quantify ideas? Ideas are objective entities, not conducive to empirical research. The appeal of this book lies in the juxtaposition of a careful exploration and discussion of the theories behind the role of ideas in policy making and policy areas, and their detailed contextualisation. Through carefully researched contemporary examples offering single country studies, comparative studies and examples from the European Union, these 'ideas' show themselves to be a double-edged sword. Ideas are revealed as both a societal and political resource, crucial to both promoting and inhibiting policy change. A clear understanding of the impact and influences of ideas on the crucial process of policy is essential to all political scientists and analysts of public policy, as well as individuals interested in the effects on policy decisions.