This book is the first in a two-volume project that provides a social-philosophical interpretation of Martin Heidegger Being and Time as an emancipatory enterprise by arguing that fundamental ontology is essentially animated by an intent shared with critical theory, viz. to make philosophy concrete for the sake of individual and collective freedom. Focused on Division One of Being and Time, this volume argues that the possibilities of individual emancipation and self-actualization are inextricably bound to their environmental and intersubjective preconditions. An adequate ontology of the self, therefore, is possible only as a social ontology. To fulfill the emancipatory aims of fundamental ontology, however, it is necessary to show that the fact that agents are always already appropriated by society does not preclude the possibility of authentic self-appropriation. Hence, this volume critically reconstructs the core commitments of the ‘appropriative approach’ to social ontology and distinguishes between the foundational and incidental aspects of fundamental ontology. The final part is devoted to addressing important criticisms of Being and Time that have impeded a fruitful dialogue between fundamental ontology and critical theory to clear the ground for a fresh re-appraisal of the former as an emancipatory project.