The European Court of Justice, as the sole judicial institution of the European Communities, has evolved into a vigorous body asserting a strong cohesive influence upon the Member States through application of the principles asserted in the Communities’ Treaties. In this article, Lord Mackenzie Stuart examines the jurisdiction of the Court in light of recent case law. In particular, Judge MacKenzie Stuart discusses doctrines of jurisdiction adopted by the Court and the application of these doctrines to recent developments involving free movement of goods and of persons within the Communities and other Treaty principles such as equal pay for men and women.