Abstract: Despite significant research in the field of equine learning behaviours and the fact that the relationship between humans and horses relies heavily on training, our knowledge of the cognitive abilities of equids remains limited. Researchers have identified two main factors that are indispensable for the better understanding of equine learning: the anatomy and physiology of the equine visual system and the discrimination and categorisation of stimuli by equids.  The equine eye has very specific anatomical characteristics that have evolved significantly over the centuries in order to adapt to its environment. The influence of the herd behaviour as well as the primary flight response of equids has also played a major role in the development of their visual system. The adaptations of the equine eye allow them to, for example, recognize threats while grazing by maximizing the field of vision, depth perception and visual acuity from that physical position.  Recent data on the functional anatomy of the eye has allowed for more accurate interpretation of previous studies on equine learning and the performance of visual tasks. Limitations to the study of equine behaviour remain, however, evidence of the detailed retinal structure and the time required to train horses for carrying out these studies reliably. Current evidence has established that stimulus position as well as size, colour and level of brightness have significant effects on equine visual acuity. This knowledge needs to be expanded upon as well as consistently applied both in the interpretation of existing evidence and in the design and implementation of new studies. A thorough knowledge of the horse's visual system is necessary for understanding, interpreting and, above all, improving interactions with the equine species, regardless of the discipline practised and further studies are necessary to improve our understanding of equine learning behaviours.