In examining the concept of “lifeworld” in Husserl’s Krisisschrift and the analysis of “Being-inthe- World” in Heidegger’s Sein und Zeit, this article establishes a convergence between the endeavors of both authors concerning the foundational problem of the pre-reflexive world, which is either a transcendental (Husserl) or an ontological (Heidegger) issue. In renouncing the transcendental concept of the world as opposed to a constituting subjectivity in favor of a conception of the lifeworld or “Being-in-the-World”, both authors nonetheless need, despite their theoretical disagreements, to fulfill the foundational function of a constituting subjectivity in order to constitute the lifeworld. Our main task will be then to investigate their solutions to the possibility of establishing an all-encompassing foundation of the lifeworld from within its very immanence and pre-reflexivity.