What makes a capital city? In this first comprehensive look at the architectural and urban visions for a European capital, Hein examines how these visions compare to the reality of the three headquarter cities for the European Union - Strasbourg, Luxembourg, and Brussels. Tracing the history of the EU and its creation of the new political entity of the polycentric capital, Hein explores the impact that European unification has on visionary projects and the transformation of EU member cities. Widely researched, the book also brings in architectural projects that have remained largely unknown until now. Using architectural and urban history as a lens, Hein examines the past five decades of European unification. Also analysed for the first time are the debates, plans, projects, and constructions, both realized and failed, that accompanied this process. Looking to the future, Hein asserts that the task of these three capital cities is to balance the needs of a collective Europe with national, local, and - increasingly - regional demands.