Boredom, while often casually attributed to non-human animals by both laypeople and scientists, has received little empirical study in this context. It is sometimes dismissed by others as anthropomorphic or a trivial concern in comparison to other welfare problems faced in captivity. Recent work on human boredom, however, has led to evidence that, far from being trivial, it can have serious consequences in the form of risky behaviour and reduced physical as well as mental health, and potentially contributes to social problems. Research on mink, supported by older literature on farm and laboratory animals, suggests that monotonous, stimulus-poor environments can induce an increased motivation for diverse stimuli, consistent with the experience of boredom. This experience is likely to be aversive and may lead to problems such as depression-like states or self-injurious behaviour if not addressed. Boredom should therefore be treated as an important welfare concern. Research is needed to find practical ways of identifying this state and to determine how widespread it is across species and which animals are most at risk. Possible ways of alleviating or avoiding this problem include offering animals in our care a choice in the level of stimulation they experience and opportunities to experience appropriate cognitive challenge.