Stereotypies are repetitive, invariant behaviors with no apparent goal or function, often observed in captive animals, mentally ill or handicapped humans, and those given stimulant drugs. They are typically associated with sub-optimal environmental conditions and have been used as indicators of poor welfare. Stereotypies can develop from frustration, stress, or lack of stimulation, and may persist due to reinforcement or other mechanisms. Empirical evidence suggests that stereotypies are linked with reduced awareness of external events, lower arousal, and distress, but the relationship is complex and often correlational. Some stereotypies may serve as coping mechanisms, providing sensory input, reducing arousal, or releasing endogenous opioids, while others may not have any beneficial consequences. The persistence of stereotypies can be explained by reinforcement, positive feedback, or other factors, and their properties vary across different species and contexts. Overall, while stereotypies are often seen as abnormal, their function and impact are multifaceted and require further research to fully understand.Stereotypies are repetitive, invariant behaviors with no apparent goal or function, often observed in captive animals, mentally ill or handicapped humans, and those given stimulant drugs. They are typically associated with sub-optimal environmental conditions and have been used as indicators of poor welfare. Stereotypies can develop from frustration, stress, or lack of stimulation, and may persist due to reinforcement or other mechanisms. Empirical evidence suggests that stereotypies are linked with reduced awareness of external events, lower arousal, and distress, but the relationship is complex and often correlational. Some stereotypies may serve as coping mechanisms, providing sensory input, reducing arousal, or releasing endogenous opioids, while others may not have any beneficial consequences. The persistence of stereotypies can be explained by reinforcement, positive feedback, or other factors, and their properties vary across different species and contexts. Overall, while stereotypies are often seen as abnormal, their function and impact are multifaceted and require further research to fully understand.