Originally from Take the Witness: Cross-Examination in International Arbitration, 2d Ed.

The expert witness on law plays an especially critical role in international commercial arbitration. The evidence that the witness adduces will in many cases pertain directly to the substance of the legal principles that the arbitrators will in turn directly apply to the merits of the dispute. Foreign law expert witnesses of course play an analogous role in national court litigation. Some of the challenges facing the expert witness and the lawyer examining him or her will be essentially no different in the two contexts, but others will.

What is said in the pages that follow is sometimes addressed primarily to the legal expert himself or herself, and sometimes to the attorney who will be examining or cross-examining him or her. The truth is that every observation made here is one that entails lessons for the expert and the attorney alike.  This chapter does not deal with the situation in which an arbitral panel appoints its own legal expert.  It remains unusual for international arbitral tribunals to appoint independent legal experts; even international arbitrators who come from systems in which court-appointed foreign law experts are the norm will be comfortable in having expert legal opinion come before the panel through experts retained by the parties. Moreover, should the legal expert be a person of the tribunal’s choosing, rather than party-retained, the entire dynamic will be altered.  Counsel will want to treat the panel’s expert no more roughly than counsel treats the panel itself.

The most important set of characteristics that an effective legal expert can exhibit – not only on cross-examination, but also on examination and in written submissions – is (a) a demonstrated mastery of the law, and notably of the relevant field of law within that legal system, (b) an uncompromising integrity in his or her exposition of the law, (c) skill at exposition, and (d) a professional temperament.  Ideally, a legal expert will bring all these attributes to the table in full measure without need of urging by counsel.  But that will not always be the case.  It is in counsel’s interest throughout the proceedings to consider whether the expert is adequately demonstrating these attributes to the panel and, if the expert is not, to offer him or her the appropriate admonitions.