Strange repetitive behaviors in confined animals (including those sometimes called stereotypies) have been used as welfare indicators because they are disturbing and fairly easy to assess. it is not certain which behaviors should be included (for example, is wheel-running normal or abnormal?) or how much the heterogeneity of different forms matters, and so I use the deliberately vague term "abnormal repetitive behavior" (ARB) in place of stereotypies. But despite these unknowns, enough is now understood to use ARBs in welfare assessment (where welfare means affective state: moods, and quality of life). To evaluate the validity of ARBs as indicators of welfare, I will review whether they are increased by exposing animals to aversive stimuli and stimuli that are ancestrally bad for fitness. I will show that the prevalence and/or frequency of ARBs typically reflects suboptimal husbandry and uncomfortable clinical conditions, and that they are quite specific to negative states (though perhaps as experienced over the lifetime, rather than just the present state alone). Thus, ARBs are reliable signs of poor welfare. However, bouts of ARB are not necessarily triggered by negative states. So, it is best to use ARB to assess chronic states, not moment to moment changes. Furthermore, general activity can by a confound. Indeed, some negative states never promote ARBs; and in some species, strains and individuals show little ARBs, even in extremis, becoming inactive instead (such that all else being equal, we should not assume that high ARB individuals have worse welfare than low ARB individuals). Together this means that ARBs have poor sensitivity to negative welfare, being prone to false negatives when used as welfare indicators. The absence of ARB is therefore necessary but not sufficient for inferring good welfare. This webinar will prepare attendees how to use ARBs in the welfare assessment of laboratory primates, rats and mice.