This article argues for a mutation in how mental health is conceived in the early twenty-first century. In this mutation, physical environments, in the form of homes, workplaces, and streetscapes, are understood as central to the production and maintenance of good mental health. Much writing on this topic has taken place within a rhetorical division between stereotypically urban buildings or spaces (tower blocks, for example), which are said to be harmful to the human mind, and idealized rural or green spaces, such as parks or small hamlets, understood to be psychologically restorative. This discourse, which has its roots in both cultural and scientific developments, has rendered mental disorder as, at least in part, a spatial problem—which is to say, as a problem that might be both understood through but also treated by spatial practices. The goal of the article is to establish the ground of this claim and to make some of its epistemic roots visible. The article begins with an ethnographic account of a contemporary intellectual movement aimed at populating urban spaces with trees in the name of global mental health. Then the discussion turns to a series of critical developments in the psychological and neurobiological sciences—the article demonstrates how these, in turn, are efflorescing into new links between the architectural and psychological sciences. The article shows how this scientific discussion is paralleled by developments in urban planning—Ebenezer Howard's program of the early twentieth century, set out in Garden Cities of To-Morrow, is taken as exemplary here. The article ends with a reading of Clive Barker's 1985 short story “The Forbidden” and of the film Candyman, which it gave rise to, whose shared sense of horror at the visceral consequences of failed urban experiments, I argue, should be read as a critical inflection point for the contemporary relationship between psychology and architecture.