This book addresses the process of judicial cooperation in the field of criminal justice, and poses questions on possible harmonisation across the European Union. An expansion of European sovereignty and European jurisdiction relating to criminal matters - domestic crime as well as transborder crime - should be considered as an extension of political approximation and harmonisation by judges of supranational courts and, possibly, by domestic judges. Therefore, the relationships between the supranational courts (the European Union’s Court of Justice and the Council of Europe’s Court of Human Rights) and domestic courts in the English and Welsh criminal justice system and the Italian criminal justice system are explored in detail. The difficult judicial dialogue between the European and the national strata is considered. An examination of the lack of a horizontal judicial dialogue between the two nation-states, combined with an inconsistent, vertical, judicial dialogue between the nation-states and the two European courts, highlights the resistance between national sovereignty and European sovereignty in this area.