The growth in number of studies on Human-Animal Interactions (HAIs) and Human-Animal Relationships (HARs) in zoos is relatively recent, but also fairly substantial, so that there are now over 60 peer-reviewed publications dealing with this topic. Almost exclusively these studies have been done to inform our judgements about the welfare of zoo animals, and how it is influenced by human presence and human contact, with a small number of studies being concerned with potential conservation consequences of this. By contrast, little attention has been paid to what HAI/HAR studies in zoos can tell us about Animal Behaviour, even though behaviour is the primary measure of welfare used in most of these studies. Here I consider what zoo HAI/HAR studies can contribute to a wider understanding of animal behaviour. This contribution includes: establishment of ethograms and other behavioural descriptions for a range of exotic species which might otherwise not be studied; helping us to understand the behavioural processes involved in domestication and other adaptation to human environments; aiding our assessment of how observer presence might influence results of studies on free-living animals; contributing to our knowledge of how ecotourism might affect animal behaviour; and providing us with a window into the animal’s mind with respect to its ability to classify different kinds of people, and more widely, different categories of relationship.