The European Court of Justice (ECJ) plays a unique and crucial role in the functioning of the Community. In a community comprising twelve Member States, 13 legal systems and nine official languages, it has to ‘ensure that in the interpretation and application of this [the EEC] Treaty the law is observed’ (Article 164). It is given a wideranging role, being required by various articles to act as an international court (Article 170), as an administrative court (Articles 173-6, 178, 184), as a civil court (Article 215), as an industrial tribunal (Article 179), and as a transnational constitutional court (Article 177). The work of the ECJ has rightly received a great deal of detailed attention but this chapter will only attempt to present an outline of its composition and organisation, and the main types of work which it performs, together with some assessment of the role it plays in the development of Community law. The chapter concludes with a brief comment on the impact of the ECJ’s jurisprudence on the English courts.