This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book looks at the European Union's (EU) actorness, providing an analysis from different angles: the EU's mandate and policy, foreign policy apparatus behind it and the instruments it deploys, and its self-presentation towards and the recognition it receives from partners. The book examines Europe's distinct approach in light of the EU's ambitions to prove its actorness in international relations, its unique policy-making processes, and the interaction between member states, various EU institutions, and third countries. It considers the European and transatlantic sanctions policies as a critical instrument not only on the Iran file itself but also for the EU's actorness and the – often-disputed – effectiveness of its actions. The book focuses on the external dimension of actorness that is the approach of third countries – here: the United States – towards the EU and the subject matter, Iran's nuclear program.