Proper testing of evidence, including witness testimony, is key to ensuring due process and procedural fairness, and affirms the legitimacy of systems of international dispute settlement resolution. In this regard, commentators have emphasised that, in international dispute settlement, less weight should be given to witness testimony that has not ‘undergone the interrogation of the court and the cross-examination by the opposing party’. The WTO dispute settlement system sees some of the most active and complex litigation across international tribunals. Yet, the WTO’s standard procedural rules provide no opportunity for the adjudicator or parties to (1) request the appearance of a witness, or (2) pose live questions to the witness. Consequently, most WTO disputes do not involve any in-person testing of witnesses. In this context, this chapter sets out to suggest an approach to fill the gap in the WTO rules on in-person witness testing.