This thesis gives insight into the social ontology of Jean-Paul Sartre which counts as one of the essential and most authentic aspects of his philosophy. Aside from the phenomenologicalontological analysis of concrete human relationships of which his capital work Being and Nothingness is known, the thesis is also focused on elaborating key terms and ideas which are necessary for understanding his social ontology as well as his philosophy in general. Referring to his early essay The Transcendence o the Ego and his first comprehensive work The Imaginary, the thesis shows how Sartre started with his philosophical independence by criticizing some of the fundamental premises in the late phenomenology of Edmund Husserl. Sartre refuses his transcendental phenomenology in favour of a concretised phenomenology which will serve ontology as its method. Clearly, there are parallels with the philosophy of Martin Heidegger, but the work does not focus on the overlap between Sartre and Heidegger. The thesis is more focused on the area of social ontology where their thoughts are completely different. The same goes for the relationship between the philosophy of Sartre and Merleau- Ponty. Therefore, the work shows Sartre's ontology of conflict compared with Heidegger's concept of Mitsein and Merleau-Ponty's concept of embodied reversibility. The work points out Sartre's focus on the analysis of concrete situations and human relationships, as well as the differences compared to the more abstract analysis of human sociality taken by Heidegger and Merleau-Ponty. A comprehensive and detailed display of Sartre's famous analysis of the look is followed by other social-emotional phenomena such as shame, sadism, masochism, love, hate, death and anguish, which are also illustrated in the work. Detailed introductory elaborations of some key concepts as the concept of consciousness, ego and imagination serve as the hermeneutical key to an understanding of these emotions and concrete human relationships.