Stress' is a term little used as yet in palaeoecological studies, but there is a need to understand this concept. Stress refers to mainly environmental challenges to organisms and may be mild or life threatening. Reactions to stress may be acute and structural, or slow subtle and more long term, beginning with behavioural or physiological responses but leading to immune problems, disease and possibly death. Stress situations may be complex and not easy to detect in archaeological material. However, as stress is linked to adaptive microevolution in all species, it is a concept to be always kept in mind in palaeoecological interpretation.