The intervention of States in legal proceedings touches upon some of the
most beguiling questions in international dispute settlement. These
include questions of treaty interpretation, obligations erga omnes, the
sources of judicial power and rulemaking, the nature of incidental
proceedings, the Monetary Gold doctrine of indispensable parties,
cross-fertilization between judicial and arbitral bodies, and principles
of jurisdiction, party autonomy, and res judicata. As jurists and
scholars tend to address these questions in isolation, however, each
development in third-State practice has raised unimagined issues of
first impression-such as the 2022 declarations of dozens of States
exploring mass intervention before the International Court of Justice in
Ukraine v. Russia, and the participation of neighbouring States without
China's presence in the 2016 South China Sea arbitration. By applying
conceptual, comparative, and historical approaches to international
justice, this book instead offers a uniquely holistic assessment of the
practice and prospective development of intervention.