Polygonal mesh has been the major surface representation of 3D objects for many years. However, enormous amount of polygons may be required for highly detailed objects, which causes very low rendering or processing efficiency. As a frequently used pre-processing technique for a large variety of geometric processing applications, polygonal mesh simplification has been considered as one of the most important fundamental techniques. In this book, the issue of polygonal mesh simplification, in particular, for large meshes are studied and a number of high-performance approaches are proposed.