The reader will find basic knowledge about the degradation of polymers, its causes, course and consequences in a broader context, as indicated through the list of the chapter titles: Introduction; Depolymerization; Initiated cleavage (degradation) of macromolecules; Thermal degradation; Photochemical degradation; Mechanochemical degradation; Oxidative degradation; Polymer burning; Kinetics of cleaving macromolecules when chain depolymerization is negligible; Degradation in polymer recycling; Protection of polymers against degradation.