Publisher Summary This chapter considers a completely different sort of reasoning task. One type of reasoning dictates about causes and effects where abductive reasoning appears especially useful is diagnosis. The goal of diagnosis is to find a disease (or diseases) that best explains a given set of observed symptoms. Typically, a disease contains a small number of well-known symptoms, but a symptom can be associated with a large number of potential diseases (for example, fever can be caused by hundreds of afflictions). In addition the chapter also describes the term Resolution that can be shown in the propositional case. Resolution is complete for nontautologous prime implicates. The way of handling explanations suggests that it might be a good idea to precompute all prime implicates of a knowledge base (KB) using Resolution, and then generate explanations for a literal by consulting this set as needed. The applications of abductive reasoning in order to object recognition and plan recognition are also considered in the chapter.