Chapter 3 describes the anatomy of medical uncertainty, identifying key attributes that give it a three-dimensional conceptual shape, form, and structure. It characterizes uncertainty in terms of its (1) fundamental sources (root causes), (2) issues (substantive problems), and (3) loci (persons in whose minds uncertainty resides) and presents a conceptual framework that allows the variety of uncertainties in medicine to be classified and better understood. The chapter makes the case that in all of these ways, a three-dimensional conceptual framework can facilitate a more intentional, targeted, and rational approach to evaluating medical uncertainty. By providing a way of visualizing, ordering, and objectifying an otherwise invisible, disordered, subjective reality, the framework can ultimately enable clinicians and patients to better manage medical uncertainty.