Five challenging Dutch criminal cases and accompanying Supreme Court judgments form the starting point of this book. They are used as the primary stepping stone of a description, as well as a comparative analysis, of the law on criminal participation in five prominent European countries. These cases concern disputable aspects of criminal regulations applicable to situations in which persons 'Act Together in Crime.' All cases focus on joint perpetration, criminal aiding, or both, and their outcomes have provoked strong debates among legal scholars and practitioners in the Netherlands. The book starts with a description of the cases, followed by an extensive overview of the Dutch law on criminal participation. Criminal law experts from France, Germany, Austria, and Italy each present their nation's law on joint perpetration and criminal assistance, alongside their analyses of the five cases. The book concludes with an overall comparative perspective of the different outcomes to the cases and reflects on the different systems of criminal participation in the aforementioned countries. This study seeks to give legal scholars, practitioners and lawmakers a valuable insight in the differences and similarities in how five distinct European criminal law systems deal with one of the most challenging criminal law topics. This research was carried out by a network of experts from Austria, France, Germany, Italy, and the Netherlands. (Series: Groningen Centre for Law and Governance) [Subject: Criminal Law]