Nonsignatories

Nonsignatories are individuals or entities that did not sign a treaty or contract but may be bound by it or may acquire rights under it under certain circumstances. In international law, a treaty typically binds only its signatories. However, various theories and doctrines allow non-signatories to be affected by or committed to treaty obligations.

Common mechanisms by which nonsignatories may be bound include attribution or vicarious liability (agency or alter-ego theories), the group of companies doctrine (where corporate affiliates are treated as part of the same economic unit for the purposes of treaty obligations), and cases where consent is found through estoppel or waiver (for example, where a non-signatory has benefited from the treaty regime or participated in related negotiations). In some contexts, successor-state or state-cession arrangements can also extend treaty duties to entities that did not sign the original instrument.

In the field of investor-state arbitration and related areas, tribunals have sometimes recognized that non-signatories can be bound by consent to arbitrate through relationships with signatories, shared investments, or umbrella clauses that extend obligations to related parties. These developments are debated, with arguments balancing the goal of effective protection under international agreements against the primacy of explicit consent.

In domestic contract law, non-signatories may be bound by arbitration clauses or other contract provisions through theories of agency, estoppel, or third-party beneficiary status, as well as through assignment or novation in appropriate circumstances. The question of whether a nonsignatory should be bound is typically resolved by examining the specific treaty text, applicable national law, and the factual relationships involved.