Did you know NATO is not one but several international organizations operating under a single institutional roof? This book offers the first comprehensive international institutional law analysis of NATO's transformation from a Cold War alliance into a dynamic, sui generis institution. Drawing on newly declassified UK and US archival material and reconstructed travaux préparatoires, it reveals how NATO’s legal positions developed different legal personalities, a hybrid regime of privileges and immunities, and a unique responsibility framework. You will discover how Article 9 of the North Atlantic Treaty enabled an institutional revolution — and, finally, why American commitment remains legally, institutionally and strategically indispensable. Essential reading for international law scholars, diplomats and NATO practitioners alike.