This book offers an exciting overview of how the investor-state dispute settlement mechanism currently deals with allegations and/or evidence of fraud and corruption. It provides a detailed analysis of the legal framework under which arbitral tribunals usually operate in investment disputes involving allegations of illegality. Readers will find step-by-step examinations of the corruption and fraud arguments employed by arbitral tribunals in ten landmark ISDS cases, followed by a chapter summarizing the status quo on the topic. The final part of the book discusses the identified challenges of addressing illegality issues in investment arbitration and potential solutions, including the creation of a multilateral investment court.