In design problems, earlier cases can almost never be reused exactly, but must be adapted to new speci cations. Since a design is a physical object, it must rst be modelled in order to be manipulable by computer. In particular, we consider models which identify variables and constraints on their relative values (see Figure 1). The choice of these abstractions has a large in uence on the complexity of adaptation: a very general model will have many variables and constraints, thus making adaptation a very complex process. A model which is only tailored to the particular di erences in speci cations will make adaptation much more manageable. It is thus desirable to formulate abstractions with reference to particular cases and new design speci cations. We have used case-speci c abstractions for adaptation in two projects of case-based design: CADRE (Hua et al., 1996]) and FAMING (Faltings and Sun, 1996]). A brief and readable documentation of both systems together can be found in Faltings, 1996]. In this extended abstract, I brie y discuss the use of abstractions for case adaptation in the two systems.