The basic principle underpinning case-based reasoning (CBR) is that new problems can be solved by reusing solutions to past problems. The generality of this idea means that CBR is finding application in a wide variety of areas. The special advantage of CBR is that a case can be a very convenient means of capturing knowledge, especially in weak theory domains where the relationship between causes and effects may not be well understood. Cases may embody more than problem-solving knowledge; the knowledge in a case may be a creative structure or a complex behavior pattern. The widespread applicability of this idea means that it has been exploited in a diverse range of areas across the arts and sciences. This article provides a brief summary of some of these applications.