Ignorance represents a situation in which some potential outcomes are not even identified. Often they are both unknown and unknowable. On a continuum that begins with risk and progresses through uncertainty, ignorance is the third, final, and most extreme state in the sequence. “The anatomy of ignorance,” introduces a medical metaphor. Analysis diagnoses ignorance as a malady that inflicts significant damages at the individual and societal levels. Fortunately, as with many maladies, understanding ignorance can help us recognize its presence and treat it more effectively. Primary ignorance denotes the failure to recognize that one is ignorant and that highly consequential potential outcomes loom that cannot be identified. Literary fiction leads us into truly interesting territory in terms of complex decision making with idiosyncratic variables. Learning about ignorance has important implications. Once ignorance becomes a part of the decision-theoretic discourse, decision scientists can develop methods and train decision makers to cope with it.