It is the goal of my dissertation to explain our peculiar aesthetic fascination with architectural ruins and to show why ruins are worthy of our time and aesthetic appreciation. I propose a model of aesthetic appreciation specific to ruins, one that not only presents a methodology of interpreting and evaluating ruins, but also suggests how we ought to preserve and display these objects of immovable material culture. I discuss four key examples: Bannerman Castle (Fishkill, New York), Mỹ Sơn Archaeological Site (Quảng Nam Province, Việt Nam), Gas Works Park (Seattle, Washington), and the recent “rust belt” ruins (Detroit, Michigan). Before proceeding to my aesthetic account I propose a definition of “ruins”—a difficult task for many reasons. Foremost, it is not clear when a structure sufficiently decays to become a ruin or when a ruin sufficiently decays to become a pile of rocks and cease being a ruin. This is a classic example of the sorites paradox. If one seeks a definition of “ruins” that delineates such rigid markers as necessary and jointly sufficient conditions, the project is hopeless. I define “ruins” from the perspective of social ontology, where I argue these objects are partially constituted by their communities viewing them as such. The literature I draw upon is interdisciplinary. Philosophical, literary, museological, and art historical texts buttress my contemporary account of ruins appreciation, which encompasses ruins of antiquity as well as modern-day ruins. I argue that the role of the picturesque in ruin appreciation has been overemphasized, while the role of ruins in theories of the sublime has been underemphasized. Ultimately, however, I argue for a pluralistic account of the aesthetic value of ruins. My account of ruins provides a unique framework for the ethical identification, preservation, and consumption of ruins. If we see ruins as in the process of decay, and we have good reasons to respect the aesthetic integrity of ruins, we ought to allow a ruin to ruinate. Paradoxically then, in order to “preserve” the special aesthetic value of a ruin, we should allow it to decay. Another paradox centers on ruin appreciation, which historically has been wedded to tourism. While all tourism provides challenges for ruin preservation, contemporary ruins face unique worries of exploitation, exploitation of descendant and co-existent ruin communities as well as exploitation of the ruin itself.