Architecture and philosophy are no strangers to one another. In philosophical writings, architecture appears referred to, spoken of, described, defined, categorized, and figuratively used. In architectural discourse, by theoreticians and practitioners alike, philosophy appears in syllabi, bibliographies, in the formulation of design concepts, or their critique, or broader theory, through quotes or references to philosopher’s names, works, and terminology, not to mention in the commonplace expression “a philosophy”. Architecture and philosophy, in their multiple conceptions and formulations, across authors, movements, styles, schools of thought, and epochs up to the present day, have and continue to engage one another. The very fact of this engagement, however, rarely appears as an issue in itself. Why does architecture reach out to philosophy? Why does philosophy address architecture? How does or ought this contact occur, if it ought to at all? What are the promises, potentials, and problems contained in their intersections? And what is meant by this notion that has yet to be pinned down with approximate but unsatisfactory words like “engage”, “reach out”, “address”, “intersect”, or rather by a categorical slash, both splitting and joining, affirming difference while gathering it, as “architecture/philosophy”? Grounded on a broad historical overview of both disciplines’ relation, and of their increasing but still scarce thematization in recent scholarship, this thesis analyzes three case-studies of architecture and philosophy’s direct consequential interaction in the late 20th century – a particularly intense moment of exchange, when architects’ self-critique sought out contributions from philosophical insights, while philosophers’ own self-questioning led them to tinker with architectural discussions. First, the overlaps between Martin Heidegger’s philosophical project and vital architectural issues, in Being and Time (1927), “The Origin of the Work of Art” (1935/6), but principally “Building Dwelling Thinking” (1951); which historian and theoretician Kenneth Frampton carefully integrated as inalienable components of his own thinking, in the editorial “On Reading Heidegger” (1974) and subsequent texts like “Towards a Critical Regionalism: Six Points for an Architecture of Resistance” (1983), “Prospects for a Critical Regionalism” (1983), and “Rappel à l’Ordre: the Case for the Tectonic” (1990). Second, Michel Foucault’s incidental thoughts on architecture, coherently reassembled from “Of Other Spaces” (1967), “Space, Knowledge, and Power” (1982), and Discipline and Punish: The Birth of the Prison (1975); and the latter’s effects, perceptible yet difficult to grasp, upon aspects of Rem Koolhaas’ renovation design for the Koepel Panopticon Prison (1979-1981), described in the text “Revisions” (1981). Third, the collaboration between Jacques Derrida, challenging and letting himself be challenged by architectural practice, and Peter Eisenman, extracting productive stimulus from deliberate misreadings of philosophy, in the design of a garden for Parc de la Villette (1985-1987), expanded upon in their book Chora L Works (1997). The unprecedented reading of each case-study brings to light heterogeneous manifestations of a consistent mutual need of architecture and philosophy to support, transform, and enrich the specific tasks of one another, while bearing witness to the necessity, pertinence, and even urgency of reflecting upon it.