This book provides a detailed analysis of the legal framework in which the energy trade between the European Union and the Russian Federation has been conducted. Using case studies of eight member states, it critically examines the EU’s ability and the duty of its Member States to conduct their external energy trade in accordance with the principle of solidarity. Providing a comprehensive analysis of the principle of solidarity as provided in the acquis communautaire of the EU, the book critically analyses the legal framework pertaining to EU-Russia energy trade to ascertain whether, and to what extent, it satisfies the requirements of the rule of law.