The climactic event in international arbitration is usually a hearing, at which witnesses are questioned and arguments made. But, unlike in U.S.- or British-oriented court proceedings, where all evidence must be accepted and evaluated in a hearing before a court or a jury, in international arbitration, evidence may be made part of the record of the case from the first pleading, where documents and even written statements of witnesses may be presented. Subsequent submissions to the tribunal by the parties, often after exchanges of relevant documents between them, may provide the tribunal with additional documents.

The "direct" testimony of witnesses at the hearing is often presented in advance through written witness statements that provide the substance of what the witnesses would have given in person through oral questioning by their counsel at the hearing. The witnesses are, however, made available at the hearing for questioning by opposing counsel and tribunal members. The result is that oral testimony at hearings is almost entirely questioning by adversaries and arbitrators.