This book investigates the mechanisms by which membership norms influence the European Union's decision-making processes regarding enlargement. Daniel C. Thomas, a scholar of international relations and European politics, utilizes a multi-methodological approach to analyze seven decades of institutional history. He argues that the criteria for state eligibility are not merely strategic or economic, but are deeply rooted in evolving normative frameworks that define the boundaries of European identity.

Experts in European studies recognize this work as a rigorous application of norm-based theory to institutional history. Readers frequently note the academic density of the prose, which serves as a specialized resource for students and practitioners of international relations.