The diverse processes of appropriation inform the basis of the descriptions of the discipline of interior architecture. This elemental feature of the subject means it is often assigned a “slippery” status 1 . At its most extreme, this perception manifests itself in the derivative view that the subject lacks a historical, theoretical, and regulatory foundation. In response, this chapter positions two things: first, that the “slippery” quality of the interior is of paramount importance: far from being a negative condition, it is a unique and fundamental feature of the subject. Second, that the substance of this spatial, disciplinary, and professional ambiguity, manifests itself primarily as a composite construct – a history, a theory, a space that is built from a number of differing ideas, objects, edifices, and other appropriated elements. This chapter will explore the idea that this ambiguous or unfixed quality manifests itself principally as an issue of semantics, and then as an intrinsic and essential spatial ambiguity. In opposition to negative associations, I would suggest that these qualities are elemental to interior architecture; they are fundamental to many aspects of the subject because appropriation and reuse – process-based approaches to formulating interior architecture – ultimately create a particular design language: one that is explicit to the thinking about and the making of “architectured” interior space.