This book offers a comprehensive analysis of the legal questions that arise for the legislative branch when implementing the crime of aggression into domestic law. Despite being the crime that gave birth to international criminal law in Nuremberg, the crime of aggression has been sidelined. It has been incorporated into domestic law by fewer than 20 States since its definition was included in the ICC Statute in 2010. Furthermore, it was omitted in the rich debate held among German scholars in the early 2000s regarding the legislative implementation of other ICC Statute crimes. The current jurisdictional inability of the International Criminal Court to respond to the Russian aggression of Ukraine invites the continuation of these academic debates without neglecting the particularities of the crime of aggression. The volume starts by assessing whether there is an obligation to criminalize aggression domestically. Irrespective of such an obligation, there is a need for implementing the crime, underscored by the book's identified normative gaps under domestic law and jurisdictional gaps under the ICC Statute. To facilitate the operationalization of domestic implementation, the book explores the technical options for incorporating the definition of Article 8bis of the ICC Statute into domestic law. It also questions how to specify the geographical ambit of domestic jurisdiction in compliance with international law, which includes the controversy about universal jurisdiction. Although it primarily deals with prescriptive jurisdiction, the book ends with the discussion of legal challenges, such as immunities, that arise when domestic courts apply the enacted laws against foreign aggressors. The volume is aimed primarily at researchers and States with an interest in the domestic implementation of international criminal law but those already working in the field should also find much of their interest contained within it. Dr. Annegret Hartig is Program Director of the Global Institute for the Prevention of Aggression and worked as a researcher at University of Hamburg where she obtained her doctoral degree in international criminal law.