There are many situations where experts are not happy to be questioned about their knowledge by people who want to write the knowledge in rules, for use in expert systems. In most of these situations, the natural way for an expert to describe his or her knowledge is through examples, stories or cases (which are all basically the same thing). Such an expert will teach trainees about the expertise by apprenticeship, i.e. by giving examples and by asking the trainees to remember them, copy them and adapt them in solving new problems if they describe situations that are similar to the new problems. CBR aims to exploit such knowledge.
Some key research areas are efficient indexing, how to define "similarity" between cases and how to use temporal information.