A great deal has been written over the years about the evidence of corruption in international arbitration. In that context, this article offers a timely analysis of some of the most contentious rules and principles applicable in relation to the evidence of corruption allegations in investment arbitration. On the basis of an assessment of forty investment awards dealing with corruption, it is demonstrated that it matters relatively little which standard of evidence is applied by arbitral tribunals. The arbitral practice also reveals that, in recent years, arbitrators have come to rely more heavily on their discretion over evidentiary matters in order to contribute to the fight against corruption. This trend has materialized not only in relation to the arbitrators’ growing reliance on their investigative powers, but also their acceptance of more flexible means of evidence for the purpose of demonstrating the reality of corrupt practices.