We present a new intuitive UI, which we call cross-boundary brushes, for interactive mesh decomposition. The user roughly draws one or more strokes across a desired cut and our system automatically returns a best cut running through all the strokes. By the different natures of part components (i.e., semantic parts) and patch components (i.e., flatter surface patches) in general models, we design two corresponding brushes: part-brush and patchbrush. These two types of brushes share a common user interface, enabling easy switch between them. The partbrush executes a cut along an isoline of a harmonic field driven by the user-specified strokes. We show that the inherent smoothness of the harmonic field together with a carefully designed isoline selection scheme lead to segmentation results that are insensitive to noise, pose, tessellation and variation in user’s strokes. Our patchbrush uses a novel facet-based surface metric that alleviates sensitivity to noise and fine details co...