The invention of ontological difference is the annex to Ontologie et temporalité, Jean Greisch's monumental integral interpretation of Sein und Zeit. The relevance of this writing is essential to understand a good part of the tensions that run through Being and time: the relationship between phenomenology and theology, the passage from Husserlian intentionality to the transcendence of Dasein (and the world) and, finally, the difference ontological or the temporal problem of being. To undertake these elucidations, Jean Greisch recovers, in the first place, the Phenomenology and Theology conference delivered in March 1927 in Tübingen, and in February 1928 in Marburg. And then he goes through the last three years of the term in Marburg in the summer semester of 1928.