Arbitration is the preferred method of resolving disputes arising out of international commercial transactions. It stands outside national legal systems because contracting parties agree in advance that they want neutral arbitrators — not local judges and juries — deciding who is at fault when a commercial relationship breaks down. But arbitration nevertheless butts up against litigation from time to time, often because one party attempts to arbitrate a matter that has been litigated to conclusion or vice versa. This article examines — through a contextual approach — questions of preclusion that thereby arise and ultimately suggests that res judicata and collateral estoppel rules developed in one context should not automatically apply in another.