While many effective automatic surface simplification algorithms have been developed, they often produce poor approximations when a model is simplified to a very low level of detail. Furthermore, previous algorithms are not sensitive to semantic or high-level meanings of models. In this paper, we present a user-guided approach for mesh simpli cation that aims to overcome such limitations. Our proposed method allows users to selectively control the relative importance of different surface regions and preserve various features through the imposition of geometric constraints. Using our system, users can produce perceptually improved approximations with very little effort.