In recent years, a new academic discipline has emerged at the crossroads of narratology and comics studies, the field of graphic narrative theory. This dissertation is an exponent of this encounter and aims to contribute to the further growth of this yound subfield of narrative theory by laying the base for a more systematic approach to storytelling in graphic narratives. The text is subdivided in four chapters, each addressing a fundamental problem. The first chapter offers some metholodigcal reflections on the study of narratives and narrativity in their/its various medial forms. It opens by outlining the possible theoretical ways of describing the interaction between narrativity and mediality. And it proceeds and concludes with an argument in favor of an intermedial narratology, that is a narratology that acknowledges the inextricability of material form and content but avoids the pitfalls of media relativism. In the second chapter, it is argued that the common understanding of comics as a sequential art tends not only to obscure the complexity of storytelling but also, due to the dualist conception of representation that underlies it, to give rise to and the perpetuate the idea that the comics medium is inherently defective. The presented alternative consists in the conceptualization of the specficity of the medium in terms of the variable relations between sequentiality, segmentivity and tabularity. This alternative presupposes the endoresment of a different conception of mimesis. The third chapter is devoted to the description of the mechanisms of perspectivization and focalization in comics. It counters the prevailing understanding of focalization in perceptual terms and advances a more elaborate and more accurate model. And the fourth and final chapter tackles the issue of visual narration in comics. It shows that the widespread assumption that images offer an immediate access to the depicted content obscures the fact that in many texts the graphic rendering or graphiation is used to mark the mediacy of the narrative. The discussion of each of these four issues makes clear that the study of graphic narratives benefits both narratology and comics studies, that the complex narrative form of comics challenges the accepted understanding of storytelling and that the terminological arsenal of narratology opens new possibilities for the exploration of comics.