 As a category, mental disorder is not well fitted to the part it plays in contemporary psychiatry. Although now widely judged to be forms of disorder (or illness), some conditions, such as those above, have not always been so understood (Porter 2002). Even when deemed to be disorder or illness, moreover, that status has frequently indicated as much ethical, as organic, deficiency (Irwin 2013). Such reminders direct our attention to contemporary medical psychiatry’s uncompromisingly biological, and avowedly value-free “medical model”, with its incumbent analogies and assumptions, and to the general question of how the taxa of psychiatric classifications are to be viewed as objects of natural science. This model has received intensive and continuing philosophical analysis and critique, including by those denying these conditions are deficiencies at all. And along with issues arising from more recent advances in cognitive psychology and the neurosciences, such foundational issues make up much of the following entry. Because of their focus on ideas central to the philosophy of mind and ethics (the relation of mind to body, and issues of responsibility and identity, for example) analyses of mental disorder have extensive implications for those fields. But as clinical phenomena, these conditions also reflect an inescapable, everyday, societal reality, giving theoretical inquiries additionally urgent practical, moral, and legal, implications.