The theoretical path of Umberto Eco (1932-2016) was that of a great intellectual who ranged from non-fiction to literary production. His was a very extensive research programme. On the basis of studies concerning aesthetics, communication and medieval thought, Eco developed it by elaborating a semiotic theory and studying language and cognition. His reflections on the method and possibilities of theoretical formulation have been crucial to his research - precisely because, as he wrote, no theoretical system comes without contradictions. Philosophers therefore do not have the task of eliminating them but rather of seeking them out where they are not apparent. This issue of Rivista di Estetica collects essays that contribute to investigating several aspects and specificities of Eco's research in philosophy, semiotics and the arts, in order to bring to light his reflection on theoretical investigation and his commitment to developing a practice that can offer important resources for today's research. It is an invitation to rethink those three theoretical fields by drawing on the teachings of this great scholar.