Virtual Arguments' subject matter is argument assistance software. Whereas word-processing software assists in the writing and formatting of texts, argument assistance software supports argumentative tasks. Argument assistance software can for instance help with the organization, visualization and evaluation of arguments. The focus of this book is on defeasible argumentation. Argumentation is defeasible when it is possible that conclusions are withdrawn in the light of further argumentation. The domain of application in this book is the law, where the defeasibility of argumentation is common and often essential. The author's approach is interdisciplinary. The book reports on current research in artificial intelligence, legal theory and argumentation theory. It is relevant for all those who are interested in defeasible argumentation, legal reasoning and argument assistance software. The book combines theoretical reflection with illustrative examples. As a result, it provides an intriguing outlook on the state of the art both for researchers and legal practitioners. Bart Verheij is Assistant Professor at the Artificial Intelligence Department of the University of Groningen, The Netherlands. His research focuses on legal reasoning and defeasible argumentation. He has studied the logic of reasoning with legal rules and with legal cases. His