My inquiry into Heidegger’s thought is justified by my profound interest regarding the fate of humanity and our planet earth in our technological age. In this research, I strongly contend that mankind in the modern technological age is homeless and rootless because of living inauthentically. I therefore suggest ways through which we can live authentically in the modern technological age. In order to achieve this aim, I borrow the notion of authenticity and inauthenticity from Martin Heidegger and Gabriel Marcel. It is my conviction that the views of these two philosophers coincide in some degree to challenge as well rescue the modern mankind from the threatening enslavement of technology and science. It goes without saying that the present book is meant to provide a genuine understanding of Heidegger’s notions of authentic and inauthentic existence in Being and Time briefly compared to Gabriel Marcel’s view in his Man Against Mass Society. To the best of our knowledge and research, the present subject ventures into a virgin field, hence its originality is far reaching as well as outstanding.