The « borderline » personality occupies a privileged, albeit highly unstable site along the edge of psychoanalysis, in more than one sense. Since the early twentieth century, it has designated the limit where neurosis fades into psychosis, and hence where what is psychoanalytically treatable gradually becomes what is treatable only by other means, if at all. Further, in confounding ways the « borderline » has entangled, through a number of important debates, perverse traits with figures of narcissism and mental health. It divides Anglo-American from French-Lacanian traditions. And it subdivides each of these two traditions from within. But the « borderline » also evokes, especially in the wake of post-structural theory and in the age of cultural studies, philosophical and historical reflections on the limits between reason and madness, science and its others, and epistemology and ethics that promise to shed some new light on these clinical concerns. And such reflections from the humanities and social sciences, in turn, risk being illuminated, implicitly or explicitly, from a clinical point of view. The current Special Issue begins to fill the glaring lack of any sustained work at the intersections of humanities border theory and the clinical discussion of the « borderline»--with essays by psychoanalysts, humanists, and social scientists of diverse methodological traditions and persuasions. Image: Mt. Etna, topographic map