Some conditions express symptoms that are neither easily visible nor measurable. Clinicians tend to highly value measurability and empirical verifiability, however. Patients with endometriosis, postconcussive syndrome, many psychiatric illnesses, chronic fatigue syndrome, fibromyalgia, and multiple sclerosis, for example, can suffer disadvantage and injustice during their health care encounters. This issue investigates ethical, clinical, and social stakes of failing to view patients and their caregivers as authoritative knowers about their bodies and illness experiences.