: A persuasion dialog is a dialog in which agents exchange arguments on a subject. In this kind of dialog, the agents disagree about the status of the subject and each one tries to persuade the other to change his mind. Several systems, grounded on argumentation theory, have been proposed in the literature for modeling persuasion dialogs. It is important to be able to analyze the quality of these dialogs. Hence, quality criteria have to be defined in order to perform this analysis. This paper tackles this important problem and proposes one criterion that concerns the conciseness of a dialog. A dialog is concise if all its moves are relevant and useful in order to reach the same outcome as the original dialog. From a given persuasion dialog, in this paper we compute its corresponding “ideal” dialog. This ideal dialog is concise. A persuasion dialog is thus interesting if it is close to its ideal dialog.