Many of the current debates about validity in psychiatry and psychology are predicated on the unexpected failure to validate commonly used diagnostic categories. The recognition of this failure has resulted in, what Thomas Kuhn calls, a period of extraordinary science in which validation problems are given increased weight, alternatives are proposed, methodologies are debated, and philosophical and historical analyses are seen as more relevant than usual. In this important new book in the IPPP series, a group of leading thinkers in psychiatry, psychology, and philosophy offer alternative perspectives that address both the scientific and clinical aspects of psychiatric validation, emphasizing throughout their philosophical and historical considerations. This is a book that all psychiatrists, as well as philosophers with an interest in psychiatry, will find thought provoking and valuable.