As is well known, Derrida's first works – The Problem of Genesis in Husserl's Philosophy, the Introduction to Husserl's Origin of Geometry, and Speech and Phenomenon – were dedicated to Husserl's phenomenology which, together with Heidegger's analysis of existence, had been since the 1930s the major reference for most important French phi­losophers of this period: Lévinas, Ricœur, Sartre, and Merleau-Ponty. Derrida found in Husserl the main themes of thought (the role of writing in science in Origin of Geometry and the conception of soliloquy and voice as self-presence in the first Logical Investigation) that constituted the basis of his project of deconstructing logocentrism and phonocentrism, as expounded in the fundamental book published in 1967 under the title Of Grammatology. But if it is clear that Derrida discovered these themes in Husserl, it is nevertheless Heidegger's thinking that constitutes not only his major reference, but the very milieu, the “element” of his philosophical enterprise. From the middle of the 1960s, with the text dedicated to Lévinas under the title “Violence and Metaphysics,” in which we find his first reading of Heidegger, until the very end of the 1990s, with “L'animal que donc je suis,” where Heidegger's conception of animality is once more analyzed, Derrida never ceased to be engaged in a critical dialogue with Heidegger's thinking. As he explained in an interview in 1967, nothing of what he attempted in this period, which was the most decisive for his entire work, “would have been possible without the opening of the Heideggerian questions,” and especially without the attention given to what Heidegger names the ontological difference, in spite of the fact that this difference seems to him to be still retained in metaphysics.