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How evidence is taken in an arbitration, and why it is not discovery
Evidence in an arbitration moves through the rulebook the parties adopted: under the IBA Rules, where they apply, a request to produce has to be narrow, relevant and material.
Published Last reviewed 7 min readBy SpyroLex
Evidence in an arbitration is taken under the rulebook the parties adopted, not under court discovery procedure. The tribunal decides the procedure where the parties have not agreed, and written witness statements and expert reports carry most of the evidence. Production runs on a request the other side may object to, and the tribunal rules on it.
Production of documents, not discovery
The word “discovery” appears in none of these texts: the IBA Rules on the Taking of Evidence, the UNCITRAL Model Law, and the ICC, LCIA and UNCITRAL arbitration rules. They speak instead of a party asking that another party produce documents, or of the tribunal ordering production.12345
The change in wording carries the difference in practice. Under the IBA Rules production is not a standing entitlement policed after the fact: one party requests it on stated grounds, the other may object on a closed list of reasons, and the tribunal decides (articles 3.3, 3.5, 3.7 and 9.2). Those Rules bind only where the parties or the tribunal have adopted them, varied them or used them as guidelines (Preamble paragraph 2 and article 1.1).2
Who decides the procedure
Procedure starts from what the parties agreed. Under the Model Law the parties are free to agree the procedure the tribunal follows, and failing agreement the tribunal conducts the arbitration as it considers appropriate (article 19). English statute says the same: the tribunal decides all procedural and evidential matters, disclosure and production among them, subject to the parties’ right to agree any matter (Arbitration Act 1996, section 34).16
The floor under that discretion is not worded the same everywhere. The Model Law requires the parties to be treated with equality and each to be given a full opportunity of presenting its case (article 18), while the UNCITRAL Arbitration Rules and the ICC Rules require a reasonable opportunity instead (article 17(1); article 23(4)).135
Written statements carry most of the evidence
Most of the evidence arrives in writing before anyone speaks. Under the UNCITRAL Arbitration Rules statements by witnesses, expert witnesses included, may be presented in writing and signed by them unless the tribunal directs otherwise (article 27(1) and (2)), and the LCIA Rules are to the same effect (article 20.3). The IBA Rules let the tribunal order a witness statement from each witness a party relies on (article 4.4), and require a party-appointed expert to file a report (articles 5.1 and 5.2).245
Oral evidence is not automatic either: unless the parties agreed otherwise, a hearing stops being optional once a party asks for one (Model Law article 24(1); ICC article 26(5)).13
Asking the other side to produce documents
The IBA Rules set the mechanism out. Each party first submits the documents it relies on within the time the tribunal orders (article 3.1), and may then submit a Request to Produce (article 3.2). The request has to do three things (article 3.3): identify each document, or describe in sufficient detail “a narrow and specific requested category of Documents that are reasonably believed to exist”; state how they are relevant to the case and material to its outcome; and state that the documents are not in its own hands, or why producing them would be unreasonably burdensome. Where the documents are electronic the request may have to name the files or search terms (article 3.3(a)(ii)), the opening for AI-assisted review.2
Article 9.2 lists the grounds on which the tribunal is to exclude a document or testimony from evidence or production, at a party’s request or on its own motion:2
- Lack of sufficient relevance to the case or materiality to its outcome
- Legal impediment or privilege
- Unreasonable burden to produce the requested evidence
- Loss or destruction of the document, shown with reasonable likelihood
- Compelling grounds of commercial or technical confidentiality
- Compelling grounds of special political or institutional sensitivity
- Compelling considerations of procedural economy, proportionality, fairness or equality of the parties2
Objections are bounded by that list: they must rest on articles 9.2 or 9.3, or on a failure to meet article 3.3 (article 3.5), so a party cannot object merely because the documents are unwelcome, though confidentiality is on the list. The tribunal orders production only where those tests are met and no ground in articles 9.2 or 9.3 applies (article 3.7). Institutional rules set a lower bar: under the LCIA Rules relevance, as the tribunal decides it, is enough (article 22.1(v)).24
Non-production has consequences inside the arbitration. Where a party fails without satisfactory explanation to produce a document it was asked for and did not object to in time, the tribunal may infer that the document would be adverse to that party’s interests (IBA Rules articles 9.6 and 9.7), and under the Model Law it may make its award on the evidence before it (article 25(c)).12
| Instrument | Ordering production | Admissibility and weight |
|---|---|---|
| UNCITRAL Model Law (as amended 2006) | No express production procedure; the tribunal conducts the arbitration as it considers appropriate where the parties have not agreed (art 19(2)), and may require a party to give its appointed expert relevant information or access to documents and property (art 26(1)) | Tribunal determines the admissibility, relevance, materiality and weight of any evidence (art 19(2)) |
| IBA Rules on the Taking of Evidence (2020) | A party submits a Request to Produce meeting art 3.3; the tribunal orders production only if the three tests in art 3.7 are met | Tribunal determines admissibility, relevance, materiality and weight (art 9.1); may exclude evidence obtained illegally (art 9.3) |
| ICC Arbitration Rules (in force 1 June 2026) | No express production procedure; the tribunal establishes the facts by all appropriate means and may summon any party to provide additional evidence (arts 26(1), 26(4)) | No express provision; the Rules govern the proceedings and, where they are silent, the rules the parties agree or the tribunal determines appropriate (art 20) |
| LCIA Arbitration Rules (effective 1 October 2020) | Tribunal may order a party to produce documents in its possession, custody or power which the tribunal decides to be relevant (art 22.1(v)) | Tribunal decides whether to apply any strict rules of evidence as to admissibility, relevance or weight (art 22.1(vi)) |
| UNCITRAL Arbitration Rules (2021) | Tribunal may require the parties to produce documents, exhibits or other evidence within a period it determines (art 27(3)) | Tribunal determines the admissibility, relevance, materiality and weight of the evidence offered (art 27(4)) |
| Arbitration Act 1996 (England and Wales, Northern Ireland) | Tribunal decides which documents or classes of documents are disclosed and produced, and at what stage (s 34(2)(d)) | Tribunal decides whether to apply strict rules of evidence as to admissibility, relevance or weight (s 34(2)(f)) |
No rule here asks a party to hand over everything that might be relevant. Under the IBA Rules a request names a narrow and specific category of documents and says how they are relevant to the case and material to its outcome, and the tribunal decides what is produced and what weight it carries.
Who rules on the evidence
Admissibility and weight are the tribunal’s in all of these texts, and the width of that discretion is deliberate: the UNCITRAL secretariat explains that it frees a tribunal from restraints stemming from traditional local law, including any domestic rule on evidence (Explanatory Note, paragraphs 34 and 35). The IBA Rules add one express exclusion the other way, for evidence obtained illegally (article 9.3).12
Where a court comes in
Courts do help with evidence, and they come second. The Model Law lets the tribunal, or a party with the tribunal’s approval, ask a competent court for assistance in taking evidence (article 27). In England and Wales and in Northern Ireland a party may use the ordinary court procedures to secure a witness’s attendance, but only with the tribunal’s permission or the other parties’ agreement (Arbitration Act 1996, section 43).17
The court’s wider evidence powers, which include preserving evidence, reach only so far as the tribunal or the emergency arbitrator, and any institution or person the parties vested with power in that regard, has no power or is unable for the time being to act effectively (section 44, as amended with effect from 1 August 2025), the same ordering that runs through emergency and interim relief.8
United States federal law routes it through the arbitrators instead, who may summon a person to attend before them as a witness and to bring any document that may be material as evidence, with the district court for the district where they sit able to compel attendance (9 U.S.C. § 7).9
Why the evidence phase is administration
None of this is improvised. Who may ask for what, what the request has to show, which objections are open and who rules on them are fixed by the rulebook the parties adopted and the law of the seat. That is the same discipline as administering a case on your own rulebook, and when an award is later enforced or challenged the question a court asks is about process.