The properties of rubbers are subject to change as a result of ageing, ultimately to the point where the material is no longer capable of fulfilling its function. After a brief introduction to the main environmental and mechanical factors affecting performance, this review focuses on the thermo-oxidative ageing of rubber. It considers the methods of, and the published results from, both natural and accelerated tests. A major section of the report is devoted to exposure and test techniques with discussion of the methods of physical and chemical analysis. An additional indexed section containing several hundred abstracts from the Rapra Polymer Library database gives useful references for further reading.