The types of damage are outlined. Symptoms and possible causes of these are discussed: damage before accessioning, e.g., before skinning and initial preservation methods; inherent reactions, that is, those between components of preserved materials such as enzymes remaining in the skin or sulfuric acid introduced during preservation; externally initiated reactions such as those caused by oxygen, water, pollutants (both industrial and from display materials) and elevated temperatures; mechanical causes including stress of weight and inadequate mannikins; pests which (including humans) cause both attrition and loss of specimens. The last section of the paper refers to documentation of damage. -- AATA