The issue Other Possible Worlds (Theory, Narration, Thought), curated by Del Zoppo, Fiordaliso, Cifariello and De Blasio, aims to investigate fiction and its frontiers, objects of critical and theoretical attention, starting from the central position they occupy in the conceptual, aesthetic, and methodological debate - for the 20th Century as well as at the beginning of the 21st. This introductory essay defines problems and theories involved in the investigation. The boundaries between fiction and non-fiction disclose connections with the invention of possible worlds in literary and artistic texts in general: utopias, eutopias, dystopias, and anti-utopias, whose peculiar strategies make them identifiable in representations and writings. The sheer number of studies and investigations focused on the relationship between fact and fiction in the last decades calls for a multidisciplinary dialogue to deepen the different meanings, messages, and aesthetic forms developed, especially in the literary field.