This work provides comprehensive coverage of the basic theories and hands-on techniques of polymer toughening, demonstrating the similarities in methods of measurement and toughness enhancement found in various classes of polymeric materials, including foams, films, adhesives and moulding grade polymers. It provides a detailed overview, from historical and current points of view, of polymer toughening as practiced in industry, and lays the theoretical groundwork for the analysis and prediction of different modes of toughening.