Much research has highlighted that sub-state entities (SSEs) - such as the German Lander, the Spanish autonomous communities, or the French regions - mobilise at the European level. This literature, however, is silent on how this sub-state activity interacts with that of its own member state. Do SSEs lobby in Brussels with their member state (cooperation), without their member state (non-interaction), or against their member state (conflict)? This book fills the current research gap by identifying what pattern of interaction between state and sub-state EU interest representation corresponds to, and by identifying what the determinants of such a pattern are. To achieve this, both quantitative and qualitative methods are employed. The quantitative section consists of regression analysis on data collected through a survey addressed to heads of regional offices in Brussels, and highlights that cooperation is the most frequent outcome, followed by non-interaction. Conflicting interest representation is the least frequent outcome. Further analysis reveals that devolution levels do not affect conflict but increase the frequency of cooperation and decrease that of non-interaction. Meanwhile, party political incongruence fails to affect conflict, decreases cooperation, and increases non-interaction. This quantitative work is complemented by a series of in-depth case study analyses of Scotland (UK), Salzburg (Austria), Rhone-Alpes and Alsace (both France). Based on over a hundred semi-structured interviews, the case studies, along with additional statistical testing, confirm the overall findings reached through quantitative means and further suggest that the effect of devolution overrides that of party political incongruence. Transformations in Governance is a major new academic book series from Oxford University Press. It is designed to accommodate the impressive growth of research in comparative politics, international relations, public policy, federalism, environmental and urban studies concerned with the dispersion of authority from central states up to supranational institutions, down to subnational governments, and side-ways to public-private networks. It brings together work that significantly advances our understanding of the organization, causes, and consequences of multilevel and complex governance. The series is selective, containing annually a small number of books of exceptionally high quality by leading and emerging scholars. The series targets mainly single-authored or co-authored work, but it is pluralistic in terms of disciplinary specialization, research design, method, and geographical scope. Case studies as well as comparative studies, historical as well as contemporary studies, and studies with a national, regional, or international focus are all central to its aims. Authors use qualitative, quantitative, formal modeling, or mixed methods. A trade mark of the books is that they combine scholarly rigour with readable prose and an attractive production style. The series is edited by Liesbet Hooghe and Gary Marks of the University of North Carolina, Chapel Hill, and the VU Amsterdam, and Walter Mattli of the University of Oxford.