This is a book about the concept of disease and the philosophy of diagnosis. The author proposes 'value-dependent realism' as a way to show how value judgements can be foundational for the practice of diagnosis without losing the sense that diseases are real entities. In the light of contemporary philosophy of science, the idea that there is a strict separation between fact and value is no longer tenable. Hence, all scientific facts have a value component. The concept of disease is itself a value-laden concept. Furthermore, when we create classifications of disease, we introduce more values. Finally, the diagnostic process necessarily involves making value judgments. This book situates the practice of diagnosis in a new vision of how values permeate the world of disease and medical practice. It will be of interest to philosophers of medicine, value theorists, bioethicists, and physicians.