This paper focuses on the main claim of Umberto Eco’s Open Work, according to which any work of art is an inherently ambiguous message, i.e. is inexhaustible, or in principle likely to be the object of an infinite number of interpretations. It does so, first, by restricting itself to the specific topic of the literary work of art, and, secondly, by making a detour, that Eco himself suggests, though he does not really explore it, via Sartre’s ontological phenomenology. This detour (...) will eventually lead the reader from Being and Nothingness to What is Literature?; from Sartre’s “theory of the phenomenon” to his description of the poetic and prosaic attitude; and from a theory of literature qua ambiguity-inexhaustibility to that of openness qua esthetic phenomenon. Finally, it is the capacity of Sartre’s phenomenology to ultimately clarify, or provide a foundation to, Eco’s own theory, as well as the latter’s originality with regard to the former, that will be studied and accounted for. (shrink)