This study of possible worlds and fictional worlds aims to provide a conceptual exposition of how the two terms relate. Since possible and fictional worlds interact both in the philosophical discipline and in the domain of literary theory, my conceptual exposition switches constantly between discourses of both. The overall task of the analysis presented in this study is twofold: for one, this study exhibits an attempt to uproot the mechanism behind interdisciplinary borrowings. The case of possible worlds supplies an intricate and at the same time, a telling example in this regard: a close analysis of the conceptual affinities between possible worlds and fiction reveals the attractive yet limited scope of usability of the philosophical concept for clarifying the literary object of research. Yet the full range of questions possible worlds legitimized, although not necessarily supplied the conceptual means for solving, can lead to a study of the structure of fictional worlds along the lines opened up by the possible worlds framework. Second, the aim of this study is to make a specific contribution to the ongoing theorizing about fiction. In this context the attempt is gradually to develop and formulate a set of conventions in terms of which the understander of fiction reconstructs a fictional world with its specific constitutive domains (of objects, characters, events, points of view and time). Since this study supports a pragmatic re-thinking on the notion of fictionality, the idea is to define this notion in terms of conventions that direct the reader in interpreting the global position of fiction vis-à-vis alternative world constructions.