This text investigates the core principles and operational mechanisms of the substantive law governing the European Union. Catherine Barnard, a professor of EU law and employment law at the University of Cambridge, provides a comprehensive analysis of the internal market, including the free movement of goods, persons, services, and capital. The work utilizes a combination of legislative analysis, case law, and academic commentary to explain how these legal frameworks function within the broader context of the EU legal order.

Legal scholars and practitioners frequently cite this work as a foundational resource for understanding the complexities of EU substantive law. Readers often note the academic density of the prose, which makes it a standard reference for law students and professionals seeking a rigorous overview of the field.