A rgumentation-which used to be an informal topic, of interest primarily to lawyers and philosophers-has become in recent years an area with a strong formal foundation, with numerous applications in cognitive science and information technology. The first communities concerned with argumentation were those interested in its relationship to reasoning by individuals (notably Stephen Toulmin and his followers) and those interested in natural dialogue and rhetoric (notably the Amsterdam school and Douglas Walton and Erik Krabbe's work). With the growing interest in argumentation in computer science, researchers have started to explore both theoretical and practical aspects in fields as diverse as mathematical logic, software engineering, and AI.From a theoretical perspective, argumentation offers a novel way of understanding and formalizing human cognition. Logicians and computer scientists are also using argumentation systems for expanding their investigations into classical forms of reasoning such as deduction and reasoning under uncertainty, and into nonclassical forms of reasoning such as nonmonotonic, modal, and epistemic logics. Another promising application area for argumentation theory is distributed AI and multiagent systems, where the dialectical nature of argumentation helps structure and reason about the exchange of knowledge and information related to claims. From a practical perspective, argumentation provides a versatile computational model for developing advanced services for decision support and for computerhuman dialogues in which explanation and rationale play a central role.Argumentation is a potentially important paradigm for developing commercial and public services that are flexible and easily understood by human users. In the first part of this article, we present our work on developing argumentation-based services for biomedical applications, with a particular focus on argument-based inference, decision making and planning. The second part of the article concerns the theoretical and practical lessons learned from this initial work and its follow-on as part of the Argumentation Services Platform with The Argumentation Services Platform with Integrated Components (ASPIC) project aims to provide advanced argumentation-based computational capabilities.