This doctoral thesis looks at the relationship between narrative space and Postmodern manifestations of the fantastic short story. The Fantastic is viewed here as distinct from other non-mimetic forms such as fantasy or science fiction, and understood as an incursion of an impossible element within a realistic frame shared by narrator and reader. The importance of narrative space in the construction of textual verisimilitude has been recurrently emphasised, especially after the so-called Spatial Turn in literary studies. However, whereas this relation between space and mimetic effect has received considerable scholarly attention, the relation between space and fantastic effect has to date not been appropriately explored, neither within the emerging field of Geocriticism nor in theoretical and thematic studies on the Fantastic. This thesis fills the existing gap, through the exploration of how narrative space is employed to disrupt the realistic effect of the literary text, i.e. the fantastic transgression as a phenomenon arising from narrative space. The frequently asked question of ‘Where does the supernatural take place?’ is substituted by those of ‘What fantastic event does space provoke? How is it rhetorically constructed? And what are its interpretations?’ To answer these questions and illustrate that this phenomenon is transnational, this study necessarily needs a comparative angle including texts from diverse socio-cultural traditions. Although textual precedents can be found, a central proposition here is that the unprecedented presence of this phenomenon is unique to the Postmodern Fantastic. Fourteen sample short stories written between 1974 and 2010 are presented as archetypical of this phenomenon and have been analysed under the light of literary theory, while also drawing from spatial theories developed in fields such as anthropology, sociology, physics and architecture. This selected corpus serves as a model for systematising literary space as transgression, structured in four chapters: ‘body’, ‘boundary’, ‘hierarchy’ and ‘world’. Paralleling narrative with an architectural piece, these four suggested categories are four basic spatial ‘steps’ in the architectural configuration of any literary work. They are four spatial principles of any realistic text, which at the same time derive from the four fundamental phenomenological and philosophical aspects of human spatiality.