Although health and disease occupy opposite ends of a spectrum, distinguishing between them can be difficult. This is the “line-drawing” problem. The papers in this special issue engage with this challenge of delineating the boundaries of disease. The authors explore different views as to where the boundary between disease and nondisease lies, and related questions, such as how we can identify, or decide, what counts as a disease and what does not; the nature of the boundary between the two categories; (...) and what sorts of considerations could justify the location of that boundary. In exploring these questions, the papers draw on detailed clinical examples, provide theoretical critiques of existing approaches to disease definition, and offer new ways to conceptualize key features in debates about disease, including harm and biological dysfunction. (shrink)