The introduction presents some general reflections on what characterises Heidegger’s fundamental ontology and what makes his thought a particularly promising point of departure for doing social ontology. I first introduce Heidegger’s holistic conceptions of Dasein and being-in-the-world by way of contrast to Cartesian atomism. I then go on to show that Heidegger conceives of intersubjectivity as a triangular relation between self, world, and other rather than a dyadic relation between two independent subjects. My claim is that Heidegger’s social ontology is found directly in his conception of the shared world and that his more well-known accounts of the Anyone and solicitude should be understood within this general framework. I also reflect on the relation between Heidegger’s social ontology and his politics and provide an outline of the book.