This book, Exclusionary Rules in Comparative Law , grew out of excellent country studies on the criminal exclusionary rule prepared for the XVIII Congress of the International Academy of Comparative Law (IACL), which was held in Washington, D.C., from July 25 through August 1, 2010. I had the honor of being the general rapporteur for criminal procedure for the congress and also chose the topic for the congress. What is controversial about what are called “exclusionary rules” in American law, prohibitions on the use of evidence ( Beweisverwertungsverbote ) in German, or simply “non-usability” ( inutilizzabilità ) in Italy, is that they end up depriving the fact fi nders in criminal trials, whether professional judges, jurors, or lay judges sitting with professional judges in mixed courts, of relevant, material evidence of guilt, because of errors committed by law enforcement personnel in the collection of this evidence. We thus have a real confrontation of two principles of criminal procedure, that of truth- fi nding, often called the principle of material truth in civil law countries, and that of “due process” to use the Anglo-American term, or the principle of a state under the rule of law or Rechtsstaatlichkeit , to use the German term.