The Unfinished History of European Integration is a companion to the history of the European Union. From the aftermath of the First World War to the EU of 27 member states and Russia's invasion of Ukraine, it guides the reader past the main events, crucial sites and key actors that shaped the EU we know today. How did it evolve from a market project to a geopolitical force, what explains the expansion of its membership, institutions, policies and the resistance to this growth, and why does it function as it does? This book provides more than just a chronological account of over seventy years of European integration. It also shows how observers past and present have made sense of the EU. The Unfinished History of European Integration is therefore a unique introduction for readers with different disciplinary backgrounds to understanding the EU. If over seventy years of European integration have taught us anything, it is that fundamental crises as well as moments of rapid institutional change have been constants in its history.