The Vienna Convention on the Law of Treaties (VCLT) - as the 'treaty on treaties' - has achieved a rich and nuanced track record of use in international law. It has now been over fifty years since the VCLT was opened for signature in 1969, and over forty years since it entered into force in 1980. As of 2022, the VCLT has been ratified by 116 States and signed by 45 others, with some non-ratifying States also recognising parts as reflective of customary international law. In the intervening decades, the VCLT has had a profound influence on the interpretation, application and development of international investment law, including in the context of investment treaty arbitration. This book presents the first consolidated analysis of how the VCLT has informed the practice of international investment law and the resolution of investor-State disputes, and the role that the VCLT may play in shaping the future of this field.

The diverse contributors to this book are scholars and practitioners from around the world, who offer a variety of perspectives on the nexus between the VCLT, international investment law and investor-State dispute settlement (ISDS). Each chapter demonstrates how approaches to key issues of treaty law in investment treaty arbitration diverge or converge from the VCLT and approaches of other international courts, as well as the lessons that investment treaty arbitration could derive - or even offer - for the interpretation and application of the VCLT rules in other settings. Their insights and analyses consider aspects such as the role of the VCLT for:

• interpretation of more specific approaches to treaty law drafted by treaty negotiators;

• treaty application in circumstances of contested State territory or succession challenges;

• temporal challenges arising in treaty interpretation;

• the status of bilateral investment treaties between European Union Member States and related termination endeavours;

• questions concerning the validity, termination and amendment of investment treaties, including as part of ongoing ISDS reform processes;

• current multilateral reform proposals, including the possibility of an appellate mechanism or a multilateral investment court;

• grappling with the challenge of fragmentation in international investment law, including the role of prior decisions in treaty interpretation, the challenges introduced by treaty conflict and the multitude of approaches that may be taken by national courts when implementing treaties like the New York Convention; and

• treaty interpretation and drafting as aided by emerging technologies, such as data analytics, machine learning, smart contracts and blockchain.

The book's appendix provides a highly valuable tabular summary of ISDS arbitral practice relating to the VCLT, collating key references from over 350 different procedural orders, decisions and awards.

By revisiting the role that the VCLT has played in the development of this field of law, this invaluable book unlocks insights into how the VCLT might be used to support its ongoing development and the resolution of the next generation of investor-State disputes.

This book is essential reading for a variety of stakeholders, including arbitrators, counsel, scholars and government officials, who will benefit from its in-depth and practical analysis of the VCLT's relevance to and impact on investment law and investor-State arbitration and its role in shaping where this field of public international law might be headed in the decades to come.