This chapter brings out the aspects of Heidegger's phenomenological ontology, early and late, that have influenced Feenberg's social phenomenology of technology. In the first part of the chapter I evaluate the influence that Heidegger's concept of the enframing (Ge-stell) exerts on Feenberg's philosophy of technology. In the second part I discuss the influence of Heidegger's early phenomenology (interpreted by Feenberg as a phenomenology of action based on the model of craftwork) on Feenberg's phenomenology of technical action. These two influences, I argue, converge in Feenberg's instrumentalization theory, later rearticulated as the functionalization theory of technology. Combining this two-tiered theory about the function and meaning of modern technical devices and production with Marcuse's call for an "aesthetic Lebenswelt" leads Feenberg to articulate a new form of rationality. This new form of rationality includes a reformation of technical design that reflects life-affirming aesthetic and political values and possibilities.