This book offers a comprehensive analysis of how the EU and NATO have worked together informally over the past decade, since formal cooperation under the 'Berlin Plus' agreement stalled.

EU-NATO cooperation has been stuck in a political quagmire since the mid-2000s, tempting many scholars to conclude that very little is going on between the EU and NATO. This book challenges the view that such cooperation is obsolete and outdated by shedding new light on a range of new informal interaction patterns that exist outside or on the fringe of formal institutions, arenas, meeting formats and procedures. In order to capture and understand the informal dynamics in EU-NATO relations, the book applies practice theory. The specific aim of the book is threefold: First, it seeks to analyse how EU-NATO cooperation has evolved despite the stalemate surrounding formal cooperation under the 'Berlin Plus' agreement and framework. Second, the book aims to add new knowledge to European security and defence studies, bringing concrete knowledge to the fore through a practice theory approach that focuses on where and how interaction is de facto taking place. Third, the book aims at adding valuable insights to the study of practice in IR in general by using practice theory to understand and explain European security cooperation.

Through a combined use of qualitative, in-depth interviews with military, civilian and police personnel and primary and secondary literature, the book identifies, maps and analyses how practitioners engage in informal staff-to-staff contacts, information-sharing, cross briefings, and mutual assistance on a daily basis in headquarters and offices (Brussels, Mons) and field missions. Although the only 'Berlin Plus' mission is in Bosnia and Herzegovina, EU and NATO practitioners engage in informal cooperation in mission areas where both organisations are running separate missions, as in Kosovo, Afghanistan, and the Gulf of Aden. By exploring and analysing these informal interaction patterns through the lens of practice theory, the book offers a new understanding of the scope, patterns, dynamics and actors involved in European and transatlantic security in general and in EU-NATO cooperation in particular. The book also argues that informal EU-NATO cooperation constitutes a trans-national 'community of practice' that cuts across institutional (EU-NATO)-, mission -, professional (military-police)-, and national boundaries. It explores how shared 'background' knowledge embedded in professional military and police education and training is creating an 'ethos' and esprit de corps that facilitates the creation and maintenance of this community.

This book will be of much interest to students of EU policy, European Security, NATO, international organisations, critical security studies and IR in general.