Textbook in PDF format Polymers and composites are omnipresent in our daily lives, enabling the lightening of structural materials and food packaging. Their performance not only depends on their chemical structure, synthesis, architecture and forming process, but also evolves over time under the effect of processes that modify – sometimes slowly but irreversibly – the structure of the material. As a result, users need to consider the maximum duration of use during which these materials will retain acceptable levels of properties. This questioning is even more crucial as it responds to societal requirements linked to limiting end-of-life waste flows and preserving the resources necessary for their production. Mechanistic and Kinetic Aspects of Oxidative Aging Polymer Aging in the Presence of Water Polymers Under Ionizing Radiations: Introduction and Basic Principles Stabilization Effect of Chemical Aging on Mechanical Properties Physical Aging by Structural Relaxation in Polymers Several Aspects of Elastomer Fatigue Influence of Polyamide 6,6 Molecular Mobility on Mechanical Behavior Statistic Approach to Polymer Network Degradation