This festschrift is in honour of a leading philosopher of argumentation. Histheories of argument structure, whilst rooted in Aristotelian philosophy, havebeen influential in computer science and artificial intelligence. His theorieshave a strong empirical side and cover much of how argument and debate isconducted. They examine how the process of exploring disagreement and reachingconsensus can be structured, and how the 'nuts and bolts' of reasoning incommunication are put together. His theories are increasingly findingapplication in computer science, where his approach to commitment based modelling of dialogue has influenced the design of protocols for software agents, and his work on argument structure is being used to guidethe development of a new, world-wide argument web.