 Argument is a central concept for philosophy. Philosophers rely heavily on arguments to justify claims, and these practices have been motivating reflections on what arguments and argumentation are for millennia. Moreover, argumentative practices are also pervasive  elsewhere; they permeate scientific inquiry, legal procedures, education, and political institutions. The study of argumentation is an inter-disciplinary field of inquiry, involving philosophers, language theorists, legal scholars, cognitive scientists, computer scientists, and political scientists, among many others. This entry provides an overview of the literature on argumentation drawing primarily on philosophical sources, but also engaging extensively with relevant sources from other disciplines.