Decision-making in the European Union before and after the Lisbon Treaty aims to assess what the changes the Treaty of Lisbon envisaged and whether these ambitions have materialised since the Treaty entered into force. It offers analyses of the past, as well as what might be the future (because some provisions will only enter into effect in the years to come). To what extent has the current decision-making process been able to address the shortcomings and challenges of the past? What has been the impact of aspects of the Lisbon Treaty that clarified pre-existing norms and structures, in some cases formalizing them, rather than introducing new changes? The authors in this book look at the interaction between formal rules and informal practices seeking to point to the interaction between the two. They find that informal practices to date typically still dominate formal rules.This book was published as a special issue of West European Politics.