The parties should file evidence in support of their claim or defence with their written pleadings. Such evidence must seek to prove or disprove facts upon which they wish to rely (Arbitration Rules 24 and 33).
Evidence filed in the written process can be documentary (e.g. exhibits, witness statements and expert reports) or non-documentary (e.g. audio and video files) (Arbitration Rule 34 (2) (b)). A party may also ask a Tribunal to conduct a site visit at a place connected with the dispute (Arbitration Rule 37(1)).
The type of evidence to be filed and the manner, form and timing of filing are usually discussed at the Tribunal's first session and set out in Procedural Order No. 1. If the evidence is in a language other than the procedural language, it must be submitted in the original language together with a translation (Administrative and Financial Regulation 30 (3) and (4)). Usually the parties agree that lengthy documents that are relevant only in part need not be translated in full unless the Tribunal requires a complete translation.
The Tribunal decides any disagreement about the admissibility of the evidence (Arbitration Rule 34 (1)). The parties and the Tribunal often agree that the Tribunal may be guided by the International Bar Association Rules on the Taking of Evidence in International Arbitration (the "IBA Rules of Evidence") when considering the admissibility of evidence and other evidentiary issues. They also often agree that, absent exceptional circumstances, neither party may file additional evidence after the submission of the last written pleading, before the oral hearing.
Type of Evidence and Other Supporting Documents
Exhibits are documents that the parties rely upon to prove or disprove facts relevant to the dispute. Exhibits should be numbered individually and consecutively throughout the proceeding. The numbers are typically preceded by the letter "C-" for the claimant's exhibits and "R-" for the respondent's exhibits.
Legal Authorities are sources of law (text of law, doctrine or jurisprudence) that the parties rely upon to prove relevant points of law related to the dispute. These are also numbered individually and consecutively throughout the proceeding, and the numbers are typically preceded by the letters "CL-" or "CLA-" for the claimant's authorities and "RL-" or "RLA-" for the respondent's authorities.
A Witness Statement is a written testimony by a person concerning facts pertinent to the dispute. The statement should indicate the sources of information on which the witness relies.
An Expert Report is an opinion by an expert witness addressing aspects of a case that may be outside of the Tribunal's expertise, e.g. on the application of a particular law, on technical matters and on the calculation of damages. The report should list the instructions on the basis of which the expert proceeded and discuss how the expert reach his/her conclusions.
Generally, each party produces its own witnesses and appoints its own experts, but the Tribunal may call upon the parties to produce further witnesses and experts if it deems it necessary (Article 43 of the Convention and Arbitration Rule 34).
Each witness statement and expert report must be signed and dated and will stand as evidence in chief unless disputed by the other party. If called for examination at the oral hearing, witnesses and experts must make themselves available (Arbitration Rules 35 and 36). If they are unable to travel to the hearing site, they may be granted leave by the Tribunal to testify by videoconference.
Demonstrative Exhibits (e.g., PowerPoint Presentations, charts and graphs) may be used at a hearing provided they contain no new evidence and identify the evidence on record relied on.
The Tribunal has the discretion to consider the relevance, weight and credibility of the evidence submitted by the parties (Arbitration Rule 34 (1)).