Heidegger famously distinguished between a philosophy that thinks and a science that calculates. According to him, modern technology allows humans to extend their domain over nature but conceals being. As a result, man is left with an anthropocentric vision of the world that only a philosophical Besinnung can transcend. Hedwig Conrad-Martius has taken a different route to the relationship between ontology and science. Instead of arguing from an opposition of Geistes- and Naturwissenschaften, she sought a dialogue between the contemporary natural sciences and philosophical traditions such as Aristotelian metaphysics. Like Heidegger, she was concerned with grasping this discussion using a concept of being, convinced that ontology could serve as a framework to address the expanding knowledge of the world that areas such as quantum physics and developmental biology presented. Unlike Heidegger, she held that the being that “can show itself from itself”, could also be found on a laboratory table. In this talk, I want to consider the relationship between ontology and science in Heidegger and Conrad-Martius. Specifically, I will ask how the different concepts of essence and essence analysis shape Heidegger’s and Conrad-Martius’ approach to a (scientific) ontology.