There is a wealth of material that shapes the law of State responsibility for breaches of investment contracts. First impressions of an unsettled or uncertain law have thus far gone unchallenged. But unchallenged first impressions point to the need for a detailed study that investigates and analyses the sources, the content, the characteristics, and the evolution of this law. The argument at the heart of this monograph is that the law of state responsibility for breaches of investment contracts has carved a unique and distinct trajectory from the traditional route for the creation of international law, developing principally from arbitral awards, and mimicking, to a considerable extent, the general international law on the protection of aliens and alien property. This book unveils the remarkable journey of the law of state responsibility for breaches of investment contracts, from its origins, to its formation, to its arrival at the cusp of maturity.