The protection of foreign investment by treaties often clashes with the State's sovereign right to investigate economic crimes committed by investors. This article examines the different approaches taken by tribunals to questions concerning admissibility and jurisdiction, applicable law, the standard of review, the burden and standard of proof and deference to actions taken by domestic courts and regulators related to economic crimes. It concludes that investors should not automatically be deprived of treaty protections and their access to investment arbitration blocked. The arbitration agreement, being autonomous from the main contract (or the relevant treaty), should, as a rule, remain valid even if the conduct of investors is tainted by economic crimes. The article calls on investment tribunals to reflect in their awards on the contributory fault of the parties when representatives of States and investors are both complicit in economic crimes. Domestic criminal proceedings may adversely affect arbitral proceedings, in particular by complicating the availability of evidence and witnesses. The practical enforcement of provisional measures in relation to economic crimes, much like any kind of provisional measure, faces its own difficulties. Despite this, tribunals may factor non-compliance with these measures into the calculation of damages.It appears that investment tribunals should pay more attention to the principle of contributory fault when representatives of both the State and the investor are complicit in an economic crime. For example, bribery usually entails misconduct of both parties--one party making an illicit payment and the other accepting it. Penalizing only the investor by rejecting its claims or only the State would seem unfair and contradict generally accepted principles of international law, such as those reflected in the ILC Articles on State Responsibility.To achieve greater legal certainty and procedural efficiency, a new generation of investment treaties and the practice of investment tribunals should draw on not only applicable domestic law but also existing sources of international law concerning economic crimes or national best practice.