The truth of Shaw's dictum that ‘those who can, do, and those who can't, teach’, is questioned by the history of commedia dell'arte in the twentieth century, in which research, practice and teaching are inextricably bound together. The significance of commedia's influence on the modern stage lies precisely in the fact that the nature of commedia cannot be defined objectively but is mediated through research and stage practice. We have to deal, therefore, not so much with commedia itself as with an ‘idea’ of commedia, a phrase I have borrowed from Kenneth Richards and Laura Richards.