Originally from Take the Witness: Cross-Examination in International Arbitration, Second Edition

International arbitration does not lend itself to a single domestic legal system.  It applies the governing law and procedural law, rules and practices that the parties have chosen for the particular contract or dispute. Recognising the differences in evidential procedures in use in different legal systems, the International Bar Association (IBA) produced the IBA Rules on the Taking of Evidence in International Arbitration:

The IBA issued these Rules as a resource to parties and to arbitrators to provide an efficient, economical and fair process for the taking of evidence in international arbitration. The Rules provide mechanisms for the presentation of documents, witnesses of fact and expert witnesses, inspections, as well as the conduct of evidentiary hearings. The Rules are designed to be used in conjunction with, and adopted together with, institutional, ad hoc or other rules or procedures governing international arbitrations. The IBA Rules of Evidence reflect procedures in use in many different legal systems, and they may be particularly useful when the parties come from different legal cultures.

Witness and expert testimony and documentary evidence are the primary focus of the IBA Rules on Evidence.  The Rules establish procedures for obtaining and adducing documentary evidence and for production of witness and expert testimony in the form of written statements, which are subject to cross-examination at the evidentiary hearing.  Since the IBA Rules of Evidence were first issued in 1999, they have been widely adopted.  Accordingly, written witness and expert statements are standard and the best way to test the veracity of those written statements is through cross-examination.