This open access book provides the first systematic study of the multiple issues relating to the investigation and prosecution of international crimes under universal jurisdiction in the EU Member States. It brings together the main findings of the UNIJUR Project, a two-year research project funded by the European Union and led by the co-editors Professor Marina Mancini (principal investigator) and Professor Raffaella Nigro (associate investigator). Cutting-edge contributions delve into the complexities of universal jurisdiction investigations and prosecutions, highlight legal constraints and practical obstacles and offer comprehensive recommendations to advance accountability for international crimes through universal jurisdiction across the EU Member States. This volume is a crucial read for scholars and students of international criminal law and EU criminal law and procedure. Bridging theoretical analysis and practical solutions, it is also an invaluable resource for EU and national policymakers, investigating and prosecuting authorities, as well as for legal practitioners with an interest in accountability for international crimes. Marina Mancini is Associate Professor of International Law in the Department of Law, Economics and Human Sciences at the Mediterranean University of Reggio Calabria, Italy. Raffaella Nigro is Full Professor of International Law in the Department of Law, Economics and Sociology at the University "Magna Græcia" of Catanzaro, Italy.