Nowadays, arbitrators are frequently confronted with the issue of admissibility of evidence that is neither manifestly unlawful nor inadmissible, but that raises some questions of fairness regarding the taking of evidence. Such is the case, for instance, of documents leaked to the public domain, or of audio / video recordings made without consent, in jurisdictions where this practice is not contrary to local law. That the principle of fairness is at the core of the arbitral procedure seems unquestionable; what is open to debate, however, is how this principle is understood and applied from one jurisdiction to another. Arbitration rules and soft law do not categorize the methods of evidence taking that could be considered as unfair, leaving to arbitrators the power to decide this issue on a case by case basis. Granted, certain issues, such as for example the test for admissibility of leaked documents, should be resolved in a harmonized way. Overall, however, given the plethora of scenarios and situations involving evidence procured in an unfair manner, the corresponding sanction can only be entrusted to the internal conviction of the arbitrators